A standard toilet is about 28 to 30 inches deep, 20 inches wide, and 27 to 32 inches tall, with a 12 inch rough-in. Those numbers are easy to find and almost never the reason a toilet does not fit. What decides fit is the rough-in, the projection from the wall, and the clearance left in front of the bowl once the door swings.
Quick answer: the four numbers that decide fit
Four measurements decide whether a toilet fits. Get the rough-in right and the other three have some give. Get the rough-in wrong and nothing else matters.
| Measurement | Typical range | What goes wrong if you get it wrong |
|---|---|---|
| Rough-in (finished wall to floor bolt center) | 12 in most common, also 10 in and 14 in | The toilet will not bolt down at all, or it sits inches off the wall with a visible gap |
| Projection (wall to front of bowl) | 25 to 31 in depending on bowl shape | The door hits the bowl, or you cannot stand up without turning sideways |
| Clear space in front | 21 in code minimum, 24 in recommended | Fails inspection, and the room feels cramped every single day |
| Seat height | 15 to 16 in standard, 17 to 19 in comfort and ADA | Nothing breaks, but the wrong choice is uncomfortable for the people who use it most |
Measure the rough-in before you shop. It takes two minutes and it eliminates most of the catalog.
We manufacture bathroom fixtures and have spent more than ten years helping homeowners, builders, and designers work out what actually fits a given room. This guide covers the measurements that decide fit, what fails at each rough-in, how to choose a height, and what to do when the space is tighter than the standard sizes assume. If you are replacing a toilet, start with the rough-in section. If you are planning a room from scratch, start with clearances.
What is the standard toilet size?
There is no single standard toilet size, but there are tight ranges that cover most residential models. The table below is the full reference set, in inches and centimeters.
| Toilet component | Inches | Metric (cm) | Details |
|---|---|---|---|
| Overall depth | 28 to 30 in | 71 to 76 cm | Front of bowl to back of tank |
| Overall width | Around 20 in | About 51 cm | Side to side, usually at the tank |
| Overall height | 27 to 32 in | 69 to 81 cm | Floor to top of the tank |
| Rough-in size | 10, 12, or 14 in | 25 to 36 cm | Wall to center of waste pipe, 12 in is most common |
| Seat height | 15 to 16 in | 38 to 41 cm | Floor to top of seat, standard height |
| Bowl height | 14 to 16 in | 36 to 41 cm | Floor to bowl rim, without the seat |
| Comfort height | 17 to 19 in | 43 to 48 cm | Floor to top of seat, the ADA range |
| Round bowl projection | 25 to 28 in | 64 to 71 cm | More compact, for smaller bathrooms |
| Elongated bowl projection | 29 to 31 in | 74 to 79 cm | About 2 in longer, more seating room |
Are all toilets the same size?
No. Toilets vary by several inches in projection, height, and width, and those differences are exactly what decide fit. What is standardized is the connection to your floor: the bolt spacing and the drain opening. That is why a toilet can be physically installable and still be the wrong toilet for the room.
Here is what is genuinely interchangeable and what is not.
| Part | Standard or varies | What it means for you |
|---|---|---|
| Floor bolt spacing | Standard | Almost all residential toilets use closet bolts on a common spacing and mount to the same flange |
| Drain outlet and wax seal | Standard | A standard flange and wax ring fit nearly every floor-mounted toilet |
| Rough-in distance | Varies | 10, 12, or 14 in. This is the number that must match your floor |
| Bowl projection | Varies | 25 to 31 in. Decides door swing and standing room |
| Seat height | Varies | 15 to 19 in. Decides comfort, not fit |
| Tank width and height | Varies | Decides whether the tank clears a vanity, a window sill, or a sloped ceiling |
| Seat shape | Varies | Round and elongated seats are not interchangeable |
Are all toilet bases the same size on the bottom?
The mounting pattern is standard, but the footprint is not. Nearly every floor-mounted residential toilet bolts to the same closet flange using the same bolt spacing, so the connection is interchangeable. The porcelain footprint that sits on your tile is not: base shapes and widths vary enough that a new toilet frequently fails to cover the outline the old one left behind.
That matters in one specific situation. If your old toilet sat on unfinished subfloor or on tile that was cut around it, a new toilet with a smaller base can expose bare floor or an old cut line. Check the base footprint before you buy if your flooring stops at the toilet rather than running under it.
Are all toilets the same distance from the wall?
No, and this is the most common fit surprise. How far the toilet sits from the wall depends on the rough-in your home was plumbed for and on the specific model. A 12 inch rough-in toilet on a 10 inch drain will not reach the bolts at all. A 10 inch toilet on a 12 inch drain bolts down fine and leaves a visible gap behind the tank.
There is a widespread misunderstanding buried in this. A 10 inch rough-in does not move the bowl closer to the wall. The flange position is fixed by your plumbing, and the bowl sits over the flange either way. What actually changes between a 10, 12, and 14 inch version of the same toilet is usually the tank: many manufacturers use an identical bowl across all three and vary the tank depth to fill the space behind it.
The practical consequence is worth stating plainly. Changing rough-in version changes how the toilet meets the wall. It does not change how much room you have in front of it.
Are toilet seats a standard size?
Toilet seats come in two standard shapes, round and elongated, and they are not interchangeable. A round seat measures roughly 16.5 inches from the bolt holes to the front edge; an elongated seat measures roughly 18.5 inches. Buying the wrong one is the single most common toilet accessory return.
Measure from the center of the seat bolt holes to the outside front edge of the bowl. That single number tells you which shape you have, and it is more reliable than judging by eye. Measure the bowl rather than the seat currently on it: if the old seat was itself a wrong-shape replacement, measuring it just repeats the mistake.
Also measure the distance between the two mounting holes. Bowl shape decides seat length, but the hardware has to line up too, and that is a separate dimension. Adjustable-hinge seats exist for bowls that fall between the standard patterns.
Some bowls genuinely fall between the two standard sizes, usually on discontinued models. If your bowl measures around 17 inches, longer than round and shorter than elongated, the big box stores will not have it. Specialist seat manufacturers carry sizes the chains do not.
Are all toilet tanks the same size?
No. Tank width commonly runs from about 14 to 20 inches and overall height from about 27 to 32 inches. Tank size rarely affects whether a toilet bolts down and frequently decides whether it suits the room. A wide tank can collide with a vanity, and a tall tank can foul a window sill, a sloped ceiling, or a wall-mounted paper holder.
Tank depth is also what determines the gap behind your toilet, and it varies between models at the same rough-in. Two 12 inch rough-in toilets can sit anything from nearly flush to well over an inch off the wall. That is normal and it is why a like-for-like replacement sometimes leaves a gap the old toilet did not.
If your toilet sits in an alcove or beside a vanity, measure the tank, not just the bowl, and check it against standard vanity depths and widths. Tank shape also differs between one-piece and two-piece designs, which is worth knowing before you shop.
Rough-in: the one measurement that decides everything
The rough-in is the distance from the finished wall to the center of the drain in the floor, and it is the only toilet measurement with no flexibility. Most homes are 12 inches. Older homes and some remodels are 10 or 14 inches. If the rough-in does not match, the toilet does not install.
How do you measure a rough-in?
Measure from the finished wall to the center of the closet bolts at the base of your current toilet. Three details cause most bad measurements:
- Measure from the wall, not the baseboard. Baseboard adds half an inch to an inch and will send you to the wrong rough-in.
- Measure to the center of the bolt, not the front or back edge of the bolt cap.
- Hold the tape flat against the wall. A tape angled even slightly reads long.
If there are two bolts on each side, measure to the rear pair. If the toilet is already removed, measure to the center of the flange opening.
Round sensibly. Anything between about 11.5 and 12.5 inches is a 12 inch rough-in. Plumbers do not hit exactly 12 inches and the fixtures have some tolerance.
One honest caveat: measuring an installed toilet gives you an estimate, not a fact. The bolts are not always centered on the flange. People regularly measure 12 inches with the toilet in place, pull it, and find a 10.5 inch flange underneath. If the measurement is close to a boundary and you cannot afford to be wrong, pull the toilet before you buy.
What fails at a 10 inch rough-in?
At a 10 inch rough-in, most of the catalog is unavailable to you. Standard 12 inch models will not bolt down, because the tank hits the wall before the bolts line up with the flange. You need a model explicitly sold as a 10 inch rough-in, and the selection is a fraction of the 12 inch range, usually skewed toward round bowls and basic two-piece designs.
Ten inch rough-ins are common in homes built before the 1950s and in powder rooms carved out of existing space. If you have one, confirm it before you fall in love with a model. It is also worth pricing the alternative early, because what a toilet replacement costs changes considerably once a plumber has to touch the drain.
What fails at a 14 inch rough-in?
A 14 inch rough-in fails cosmetically rather than structurally. A 12 inch toilet will bolt down fine on a 14 inch drain, and it will leave a two inch gap behind the tank. The fixture also sits two inches further into the room, which takes two inches off the clear space in front.
Here is the part most buyers get wrong. Buying a true 14 inch rough-in model closes the gap but does not give you back that front clearance. On many models the 10, 12, and 14 inch versions share the same bowl, and only the tank depth changes. A 14 inch model has a thicker tank that fills the space behind it. The bolts are still 14 inches from the wall, so the bowl still ends up in the same place.
If you are short on room in front of the toilet, a 14 inch rough-in model will not solve it. Choose a shorter bowl instead.
Why do two toilets with the same rough-in fit differently?
Because the rough-in describes your floor, not the toilet's shape. Two toilets both sold as 12 inch rough-in can differ by more than an inch in how far the tank sits behind the bolts and by two or three inches in how far the bowl projects forward. One will clear your baseboard and the other will not.
The label gets you to the right shortlist. The manufacturer's specification drawing for that exact model decides whether it fits. Every serious manufacturer publishes one, including us, and it is the document to check before you buy rather than after.
What do you do when your rough-in does not match?
You have three options, in the order we would try them.
- Buy the matching rough-in. Always the cleanest answer. Filter by rough-in first and shape second.
- Use an offset flange. An offset flange shifts the drain center by a couple of inches and can rescue a mismatch without opening the floor. It slightly restricts the drain path, so it is a compromise rather than a free fix, and it is worth a plumber's opinion before committing.
- Move the drain. The correct fix and the expensive one. It means opening the floor and reworking the waste line, which is realistic during a full renovation and rarely worth it for a toilet swap. Budget for it as part of the toilet installation cost rather than as a simple swap.
Toilet height: standard, comfort, and ADA
Standard height toilets put the seat 15 to 16 inches off the floor. Comfort height, also sold as chair height or right height, puts the seat 17 to 19 inches off the floor. The difference is two to four inches and it changes the daily experience more than any other toilet dimension.
Bowl height and seat height are different numbers, which is where most confusion starts. Bowl height is measured to the porcelain rim. Seat height adds the seat, usually about half an inch to an inch.
| Bowl rim height | Seat height with seat | Category | Best for |
|---|---|---|---|
| 14 to 15 in | About 15 in | Standard, lower end | Children's bathrooms, shorter adults |
| 15 to 16 in | 15 to 16 in | Standard height | General use, most existing homes |
| 16 to 17 in | 17 in | Comfort height, lower end | Mixed households, a middle ground |
| 17 to 18 in | 17 to 19 in | Comfort or chair height, ADA range | Aging in place, mobility needs, taller adults |
| Above 19 in | Above 19 in | Above the ADA range | Specialty only, and above the ADA maximum |
How tall is a standard toilet?
A standard toilet is 27 to 32 inches tall overall, measured from the floor to the top of the tank, with the seat 15 to 16 inches off the floor. The overall height varies far more than the seat height because tank design varies: a tall, narrow tank and a low, wide tank can put the seat in exactly the same place.
When someone asks how tall a toilet is, they almost always mean the seat. Overall height only matters when something sits above the tank.
When is comfort height the wrong choice?
Comfort height is wrong when the people using the bathroom are short or young. At 17 to 19 inches, feet dangle for many children and for adults under roughly five foot four. Feet that do not reach the floor make a toilet less comfortable, not more, and the regret is common enough that it is worth taking seriously before you buy.
Comfort height is sold as a straight upgrade. It is not. It is a trade: easier to stand up from, harder to sit properly on if your feet do not reach.
There is a simple way to test it before you commit. Sit on a few chairs around your house and find the seat height where you can keep your feet flat on the floor with no pressure under your thighs. Measure that chair. That is close to the toilet height that will suit you, and it takes about two minutes.
Our honest recommendation: comfort height in a primary bathroom and in any bathroom being planned for aging in place, standard height in a children's bathroom, and comfort height in a guest bath where adults are the users. In a shared family bathroom, size for the shortest frequent user rather than the tallest. Do not default to comfort height everywhere just because it is what new construction does.
If the need is temporary, a raised seat or a toilet support frame is usually more sensible than replacing a toilet that fits.
What does ADA actually require?
The US Access Board's ADA standards for plumbing elements set the seat height of an accessible water closet at 17 inches minimum and 19 inches maximum, measured to the top of the seat. That is section 604.4, and it is where the "comfort height" range comes from.
Two qualifications matter for a home project. First, the ADA standards apply to public and commercial facilities, not to private residences, so nothing in your own bathroom is legally required to meet them. Second, the standard itself contains a residential exception: in residential dwelling units, section 604.4 permits a seat height of 15 inches minimum to 19 inches maximum. Standard height toilets are inside that range.
The standard also positions the fixture. Section 604.2 sets the water closet centerline 16 inches minimum to 18 inches maximum from the side wall, which is a tighter window than the 15 inch minimum that residential plumbing code requires.
One thing worth saying plainly: fitting a toilet in the 17 to 19 inch range does not make a bathroom ADA compliant. Compliance covers clearances, grab bars, approach, and controls as well as seat height. If you are planning genuine accessibility rather than general comfort, treat seat height as one item on a longer list.
Bowl shape and projection: round, elongated, compact elongated
Bowl shape decides how far the toilet projects into the room, which is the second most important fit number after the rough-in. Round bowls project 25 to 28 inches from the wall, elongated bowls 29 to 31 inches, and compact elongated bowls sit between them at about 28 inches.
How much space does an elongated bowl actually cost you?
About two to three inches of projection, and it is worth being precise about where that space goes, because the common assumption is wrong. Buyers worry that an elongated bowl will cost them knee room. It does not. You sit further back on an elongated bowl relative to the opening, so your knees end up in roughly the same place. What changes is how far the front of the bowl reaches into the room.
That distinction matters because it tells you what to actually check. An elongated bowl does not make the toilet less comfortable to sit at. It makes the door more likely to hit it, and it eats the clear space in front that your building code governs. If you had 23 inches of clearance with a round bowl, an elongated one leaves you 21. If you had 21, you are now below code.
We have covered toilet bowl shapes and their differences in more depth separately. Compact elongated bowls exist for precisely this reason. They deliver most of the seating comfort of an elongated bowl in close to a round bowl's footprint, and in a tight bathroom they are usually the right answer.
Round bowl
Round bowls are the most compact option, projecting 25 to 28 inches from the wall. They suit powder rooms, guest bathrooms, and older homes where the layout leaves little spare room. In a small half bath with an inward-swinging door, a round bowl is often the difference between the door clearing the toilet and hitting it.
Pros: takes up less floor space, works in tight layouts, usually more affordable.
Cons: less comfortable for many adults, can look undersized in a larger bathroom.
Elongated bowl
Elongated bowls project 29 to 31 inches from the wall, and the extra length is noticeably more comfortable for most adults. This is the default choice for full bathrooms and primary bathrooms where the space allows it.
Pros: more comfortable for adults, feels appropriate in a full-size bathroom.
Cons: needs two more inches of clearance, can crowd a small room or block a door.
Compact elongated
Compact elongated bowls project about 28 inches and are the most useful and least known option on this list. They give you an elongated seat in roughly a round bowl's footprint, which is exactly what a small bathroom needs when the occupants are adults.
If your measurements put you right at the edge between round and elongated, look at compact elongated before you compromise on comfort.
Clearance: what code requires and what actually feels right
Code sets the floor, not the target. The residential requirements come from section P2705.1 of the International Residential Code, and the commercial plumbing code sets the same numbers. The recommended figures are what make a bathroom comfortable rather than merely legal.
| Clearance | Code minimum | Recommended | Why the difference matters |
|---|---|---|---|
| In front of the bowl, to any wall, fixture, or door | 21 in | 24 in or more | Three extra inches is the difference between turning sideways and simply standing up |
| Centerline to any side wall, partition, or vanity | 15 in | 18 in | Stops the toilet feeling wedged against a vanity or tub |
| Centerline to the centerline of an adjacent fixture | 30 in | 36 in | Governs whether a toilet and a sink fit side by side at all |
Note that the 21 inches is measured from the front of the bowl, not from the wall. That is the detail that catches people out, and it is why total depth requirements are so much larger than they first appear.
Local codes and accessibility requirements can demand more. Check your jurisdiction before finalizing a layout, and if you are laying out the whole room, start from the minimum bathroom size the fixtures actually need.
Common wall-fit problems and what causes them
Four problems account for most fit complaints after a toilet swap. Each has a different cause.
| What you are seeing | Usual cause | What to do |
|---|---|---|
| The new toilet leaves a gap behind the tank | Your rough-in is larger than the toilet is built for, often a 13.5 or 14 in drain with a 12 in toilet. The old toilet may have had a deeper tank that hid it | Nothing, if the gap is small. There is no code minimum for tank-to-wall spacing, and a gap actually helps condensation dry |
| The tank touches or will not clear the wall | Thick tile, a tiled baseboard, or trim that the rough-in measurement did not account for | Measure from the finished surface, including tile. A model with a shallower tank usually solves it |
| The door hits the bowl | Projection, not rough-in. An elongated bowl replaced a round one, or the door was always marginal | Change the bowl shape, or change the door: out-swing, pocket, bi-fold, or swing-clear hinges |
| The toilet does not line up with the flange | The flange is off-center, or the bolts sit in side slots with no adjustment range | There is usually a quarter inch or so of play. Beyond that you need a repair flange or an offset |
What to do when you only have 30 inches
Thirty inches of wall-to-obstruction space is a common tight-bathroom constraint, and it is workable. Here is how the math falls out.
With 30 inches from the finished wall to the door, vanity, or tub in front of the toilet, a round bowl projecting 26 inches leaves 4 inches of clear space, and an elongated bowl projecting 30 inches leaves none. Neither meets the 21 inch clearance requirement, because that 21 inches is measured from the front of the bowl, not from the wall.
The number you actually need is projection plus 21 inches. A round bowl at 26 inches needs 47 inches of total depth. A compact elongated at 28 inches needs 49. An elongated at 30 inches needs 51.
| Space from wall to obstruction | What fits | What to do |
|---|---|---|
| Under 47 in | Nothing, to code | Move the obstruction, change the door swing, or relocate the toilet |
| 47 to 48 in | Round bowl only | Round bowl, and consider a wall-hung toilet if you are renovating |
| 49 to 50 in | Round or compact elongated | Compact elongated is the better choice for adults |
| 51 to 54 in | Any bowl shape | Elongated fits, but check the door swing before committing |
| Over 54 in | Any bowl shape, comfortably | Choose on comfort rather than on fit |
If you are genuinely short on depth and you are already opening the wall, a wall-hung toilet with a concealed carrier buys back several inches because the tank sits inside the wall. It is a bigger job and it is the only option that changes the geometry rather than working around it. If you are still drawing the room, a 5 by 8 bathroom layout is the most common place this problem shows up, and common bathroom sizes and dimensions will tell you what you are working with.
Which toilet size fits your bathroom?
Work down this list and stop at the first line that describes your situation. For a wider view of the decision, see our guide to choosing the right toilet for your bathroom.
| Your situation | Bowl shape | Height | Watch out for |
|---|---|---|---|
| Powder room or half bath under 20 sq ft | Round or compact elongated | Standard or comfort | Door swing is usually the binding constraint, not the wall |
| Small full bath under 40 sq ft | Compact elongated | Comfort | Clearance to the vanity and tub, not just in front |
| Standard family bath, 40 to 100 sq ft | Elongated | Standard if children use it, otherwise comfort | Children's feet need to reach the floor |
| Primary or luxury bath over 100 sq ft | Elongated | Comfort | Power access if you want a smart toilet or a heated seat |
| Planning for aging in place | Elongated | Comfort, 17 to 19 in | Side clearance for a grab bar or a transfer, not only front clearance |
| Pre-1950s home | Confirm rough-in first | Either | A 10 in rough-in narrows your choices before anything else does |
Smart toilet dimensions and what they actually require
Smart toilets are not necessarily bigger than standard toilets, and the common assumption that they are longer is worth checking against real numbers. Our own ST-01 is 26.9 inches deep, 15.8 inches wide, and 18.5 inches tall, which makes it shorter than a typical 28 to 30 inch two-piece and about four inches narrower.
The reason is the tank. A tankless smart toilet heats water on demand instead of storing it, so there is no tank behind the bowl adding depth and no tank above it adding height. That is why the ST-01 tops out at 18.5 inches overall while a conventional two-piece runs 27 to 32 inches to the top of the tank.
| Specification | Badeloft ST-01 | Typical two-piece toilet |
|---|---|---|
| Overall depth | 26.9 in (683 mm) | 28 to 30 in |
| Overall width | 15.8 in (401 mm) | About 20 in |
| Overall height | 18.5 in (470 mm) | 27 to 32 in |
| Weight | 106 lbs (48 kg) | Roughly 60 to 120 lbs |
| Flush volume | 1.02 gal (3.86 L) | 1.28 to 1.6 gal |
For context on that last row, the federal maximum for a gravity flush toilet is 1.6 gallons per flush, and the EPA's WaterSense program certifies toilets that use 1.28 gallons or less, about 20 percent below the federal standard. The ST-01 is under both at 1.02 gallons.
What a smart toilet does add is a power requirement. The ST-01 needs a cold water supply and a grounded electrical outlet within reach of the unit, on a GFCI-protected circuit, and the outlet has to sit to the side or the rear so the cord stays accessible after installation. Planning that outlet during a renovation is trivial. Discovering you need it after delivery is not.
Everything else is conventional. It is a floor-mounted one-piece unit that bolts to a standard flange, so the usual rough-in and clearance rules apply exactly as they do to any other toilet. Full specifications and the dimensional drawing are on the ST-01 product page, and you can see the range at Badeloft smart toilets. If you want the warmth without replacing the fixture, a heated toilet seat is the smaller version of the same upgrade.
How to measure your space in six steps
Five minutes of measuring prevents most toilet returns. You need a tape measure, a pencil and paper, and a phone to photograph what you measured.
- Measure the rough-in. Finished wall to the center of the rear closet bolts. Not the baseboard. If this number is wrong, nothing else matters.
- Measure the available depth. Wall behind the toilet to the nearest obstacle in front: door, vanity, shower, or tub. Compare it against the projection plus 21 inches rule above.
- Measure the width of the space. Side wall or fixture to side wall or fixture. You need 30 inches minimum, and you want 36.
- Check the door swing. Open the door fully and see where it lands. This is the most commonly skipped step and one of the most common reasons a technically-fitting toilet does not work.
- Confirm the clearances. At least 21 inches in front and 15 inches from the centerline to each side. Go beyond the minimum wherever you can.
- Add margin for comfort. If your numbers land right on the edge, take the more compact option. That extra inch of room is worth more day to day than a slightly larger bowl.
Photograph the space once you have measured it. It makes comparing models much easier later, and it means you are not measuring twice. If you are measuring for a full renovation rather than a swap, our guide on how to measure a bathroom for a remodel covers the rest of the room.
FAQs
Are toilets universal?
The connection is close to universal and the toilet is not. Nearly all floor-mounted residential toilets bolt to the same closet flange with the same bolt spacing and seal with a standard wax ring. The rough-in, the projection, the height, and the tank size all vary, so a toilet can be installable and still be wrong for the room.
Why is there a gap between my new toilet and the wall?
Almost always because your rough-in is larger than the toilet was built for, or because the toilet you removed had a deeper tank that filled the space. Two toilets with the same 12 inch rough-in can sit anything from nearly flush to well over an inch off the wall, because tank depth varies by model. There is no code minimum for the gap, and a small one is actually useful because it lets condensation dry rather than sitting trapped against the wall.
How much space do you need for a toilet?
You need 21 inches of clear space in front of the bowl and 15 inches from the toilet centerline to any wall or fixture on each side, which makes 30 inches the minimum width for the toilet area. Total depth is the bowl's projection plus that 21 inches, so a typical elongated toilet needs about 51 inches from the wall.
How do I know if I need a 10 inch or 12 inch rough-in?
Measure from the finished wall to the center of the rear closet bolts on your existing toilet. Roughly 12 inches means a 12 inch rough-in, roughly 10 inches means a 10 inch. Measure from the wall itself rather than the baseboard, because the baseboard can add enough to make a 12 inch rough-in read as 10.
Can I put an elongated toilet in a small bathroom?
Only if you have the depth for it, which is the bowl's projection plus 21 inches of clear space, or about 51 inches total. If you are short of that, a compact elongated bowl gives you most of the comfort at about 28 inches of projection instead of 30.
Are toilet seats interchangeable?
Within a shape, usually yes. Between shapes, no. Round and elongated seats are different lengths, roughly 16.5 and 18.5 inches from the mounting bolts to the front edge, and one will not fit the other's bowl. Measure the bowl rather than trusting the seat already on it.
Is comfort height the same as ADA height?
They describe the same range. Comfort height, chair height, and right height are manufacturer terms for a seat 17 to 19 inches off the floor, which is the range the ADA specifies for accessible water closets. ADA requirements apply to public and commercial facilities rather than private homes, so in your own bathroom this is a comfort decision rather than a compliance one.
References
- United States Access Board. ADA Standards, Chapter 6: Plumbing Elements and Facilities. Sections 604.2 Location and 604.4 Seats, including the residential dwelling unit exception. https://www.access-board.gov/ada/chapter/ch06/
- International Code Council. 2021 International Residential Code, Chapter 27: Plumbing Fixtures. Section P2705.1 General, Item 5, fixture clearances. https://codes.iccsafe.org/content/IRC2021P1/chapter-27-plumbing-fixtures
- United States Environmental Protection Agency. WaterSense: Residential Toilets. Flush volume criteria and the federal 1.6 gallon per flush standard. https://www.epa.gov/watersense/residential-toilets