Almost every toilet in North America will take a bidet. The exceptions are real but narrow, and you can identify them in about five minutes with a tape measure.
The short version: you need to check your bowl shape, your bolt hole spacing, and the flat space between the bolt holes and the tank. Get those three right and the seat will fit. Everything else on this page is detail for the cases where one of the three comes back odd.
Why bidet seats are fussier than regular toilet seats
A standard toilet seat is a hinged lid. It tolerates a loose fit because nothing depends on it sitting precisely.
A bidet seat is different in three ways. It carries a mounting plate that has to sit flat on the porcelain behind the bolt holes. It houses a nozzle that has to arrive at a specific position over the bowl. And on electric models it holds a water heater, a pump and control electronics, which makes it heavier and less forgiving of a bowl that doesn’t support it evenly.
A bidet seat mounted on the wrong bowl shape will rock, gap at the back, spray at the wrong angle, and put stress on both the seat and the porcelain. Bio Bidet is blunt about this in their own compatibility documentation: the bowl supports the seat and distributes the load across the fixture, so a mismatch can break the seat outright. Match the shape. Don’t try to make an elongated seat work on a round bowl because it was on sale.
The three measurements
You’ll want a tape measure and about five minutes. It’s easier if you take your existing toilet seat off first, though you can usually manage without.
1. Bowl length — round or elongated?
Find the two bolts at the back of your seat where it hinges. Measure in a straight line from the centre of those bolt holes to the front edge of the bowl.
- Around 16½ inches → round bowl
- Around 18½ inches → elongated bowl
Manufacturers publish slightly different bands around those two figures. Brondell calls 16 to 17¾ inches round and 18 to 19½ inches elongated. BidetKing puts round at 16.5 to 17.5 inches and treats anything over 18 inches as elongated. Coway’s ranges are 16.59 to 17.85 inches for round and 17.98 to 19.24 inches for elongated.
If your number lands cleanly in one band or the other, you’re done. If it lands in the gap between roughly 17.9 and 18 inches, check the spec sheet for the specific seat you’re considering rather than assuming.
2. Bolt hole spacing
Measure between the centres of the two mounting bolt holes.
Nearly every American toilet is 5.5 inches. This measurement is remarkably consistent, and for most people it’s a formality. Measure it anyway — older toilets, imported fixtures and some commercial-style bowls vary, and this is the measurement that quietly disqualifies a seat after you’ve already ordered it.
3. Clearance behind the bolt holes
This is the one that catches people out, and it’s the reason a toilet can pass the first two checks and still not take a seat.
Measure from the centre of the bolt holes back to the front face of the tank. You are looking for flat, level porcelain — the mounting plate has to sit on it.
Minimums vary quite a bit by brand: Bio Bidet asks for at least 1.5 inches, Coway for 1.8 inches, and Brondell will work with as little as ¾ inch. As a general rule, if you have 2 inches of flat space you have options across every brand. Under 1.5 inches, your choices narrow sharply.
Tolerances by brand
Here’s what each manufacturer publishes. These are compiled from the brands’ own fitment documentation, and they don’t agree with each other — which matters if your toilet is near a limit, because a bowl that one brand rejects may be fine for another.
| Bolt spacing | Bolt-to-tank clearance | Round bowl | Elongated bowl | |
|---|---|---|---|---|
| Bio Bidet | 5.5″ – 7.5″ | 1.5″ minimum | ~16.5″ | ~18.5″ |
| Brondell | 5.25″ – 8″ | 0.75″ minimum | 16″ – 17.75″ | 18″ – 19.5″ |
| Coway | 5.23″ – 7.9″ | 1.8″ minimum | 16.59″ – 17.85″ | 17.98″ – 19.24″ |
| BidetKing (general) | ~5.5″ standard | 1″ – 2″ typical | 16.5″ – 17.5″ | over 18″ |
The practical takeaway: Brondell is the most forgiving on both bolt spacing and tank clearance. Coway is the strictest on clearance. If your toilet is marginal on one of these numbers, that’s your ordering hint — and it’s worth phoning the retailer with your measurements before you buy rather than after.
Always confirm against the spec sheet for the exact model you’re buying. Brands revise hardware between product generations.
The four toilets that cause trouble
If your three measurements came back normal, you can stop reading here and go choose a seat. The rest of this page covers the awkward cases.
Skirted toilets
A skirted toilet has a smooth, filled-in side panel that conceals the trapway — the winding pipework the bowl empties into. They look cleaner and they’re much easier to wipe down, which is part of why they’ve become popular.
They cause two specific problems.
The bolt holes are hidden from underneath. Standard bidet mounting hardware assumes you can reach up under the bowl rim to tighten the bolts. On a skirted toilet you can’t. The fix is a top-mount kit, which lets you secure the seat entirely from above. Many current seats include one in the box; some don’t. Check before ordering, because buying the kit separately after the fact is an annoying extra step.
The tank fill valve may be hard to reach. The bidet’s water line normally tees off the fill valve underneath the tank. If the skirt blocks access, you’ll want an alternate T-valve that connects at the wall supply instead. This is a standard part and easy to source, but again, better to know in advance.
Skirted toilets are usually solvable. They just need the right two accessories.
French curve toilets
This is the one that genuinely stops some installations.
On a conventional toilet, the front face of the tank meets the bowl at roughly a right angle, leaving a flat shelf behind the seat bolts. On a French curve toilet, the tank sweeps down in a smooth concave curve to blend into the bowl. It’s an elegant look, and it leaves very little flat porcelain for a mounting plate to sit on.
TOTO states directly that a French curve may prevent a Washlet from installing at all. Bio Bidet says their seats don’t fit well on deep French curves because of the limited space near the mounting bolts. Some French curve toilets take a bidet seat; some cannot take one under any circumstances.
If you have one, two things help. Look at your toilet from the side to confirm — that concave sweep is unmistakable in profile. Then measure the flat width across the back of the bowl very carefully, because a seat with a narrow mounting plate may still work. The Infinity Eaze z3 is known for a narrow plate that fits a number of French curve models, and it comes in both bowl shapes.
With a French curve, call the retailer with your toilet’s make and model before you order. This is the one case where measuring alone isn’t enough.
One-piece toilets
Most one-piece toilets are fine. They’re a common form factor and manufacturers design around them.
The complication is that one-piece designs are more likely to combine features — a skirted base and a curved tank junction — so run all three measurements rather than assuming. And a one-piece with a deep French curve is the specific combination most likely to be incompatible.
Wall-hung toilets
Wall-hung toilets use an in-wall tank system, so there’s no exposed fill valve to tee off. Brondell’s guidance on the TOTO Maris is representative of the category: you need a plumber to provide an accessible ½-inch water supply connection for the bidet.
This is doable, but it’s plumbing work rather than a DIY afternoon. Budget for it.
Electrical requirements
This applies to electric bidet seats — heated water, heated seat, dryer. Non-electric seats and attachments need no power at all and skip this section entirely.
What you need: a three-prong grounded outlet, 15 amps minimum, GFCI protected. Every major manufacturer specifies GFCI. TOTO lists “120V GFCI electrical outlet required” on the Washlet product line.
On whether GFCI is mandatory: current electrical code requires GFCI protection for new bathroom outlets. If you have an older bathroom with a pre-existing non-GFCI outlet, a bidet seat will still work on it. Every manufacturer strongly recommends upgrading anyway, and given that this is an electrical appliance sitting in a wet environment, that recommendation is worth taking. Codes vary by jurisdiction, so check your local requirements or ask an electrician.
Cord length and direction. Most bidet seat cords run about 4 feet, which means your outlet needs to be within reach of that. Direction matters more than people expect: most cords exit from the right side of the unit as you face the toilet, but TOTO Washlets exit from the left. Coway’s Bidetmega uses a 47-inch two-way cord that can be routed to either side. If your only outlet is on the awkward side, check the spec sheet diagram before ordering — product photos usually don’t show the cord.
Power draw and circuits. Tank-style seats, which hold a reservoir of pre-heated water, peak at roughly 600 to 800 watts. Tankless seats, which heat water on demand, can peak at 1,400 to 1,500 watts. Either way, the seat only draws that during a wash cycle — a few minutes a day at most, idling the rest of the time.
In practice a shared bathroom circuit is usually fine. The exception worth knowing: a tankless seat on an older shared circuit can make the bathroom lights flicker when the heater kicks in. It’s harmless and it’s uncommon, but it’s a known behaviour rather than a fault with your new seat.
For new construction, NEC requires a 20-amp circuit with at least a 15-amp outlet. If you’re having an outlet installed, 12 inches off the floor is the usual recommendation, and it’s a job most electricians will finish in well under an hour.
Water supply
The bidet’s water line normally tees off the toilet’s existing fill valve using a T-valve, which comes in the box. You’ll want an accessible shut-off valve on the supply line — a quarter-turn valve is the easiest to operate, particularly if hand strength is a consideration.
Two situations need a different approach. On a skirted toilet where the fill valve is hard to reach, use an alternate T-valve at the wall supply. On a wall-hung toilet, a plumber will need to run a dedicated ½-inch connection.
A note on comfort and reach
If you’re choosing a bidet with mobility, reach, or hand strength in mind, two measurements matter beyond bare compatibility.
Overhang. Brondell flags this well: if the distance from the front of your tank to the front of your bowl is under 20½ inches, a round seat may sit better than an elongated one even on an elongated bowl, because the elongated seat will protrude past the bowl’s front edge. The round Swash is 19.4 inches overall; BidetKing lists round seats at around 19.2 inches. In a small bathroom, that overhang affects how much room you have in front of the toilet.
Control placement. Side-panel controls, wireless remotes and remote mounting position vary a great deal between models, and they’re worth thinking about before you buy rather than after.
If your toilet won’t take a bidet seat
You still have options.
A bidet attachment is the most common answer. Attachments sit between your existing seat and the bowl rather than replacing the seat, and they fit a much wider range of fixtures, including many curved and one-piece toilets that reject full seats. They’re also far cheaper. What you give up is warm water on most models, plus the heated seat and dryer.
A handheld sprayer mounts to the wall or the side of the tank and connects to the supply line. It doesn’t touch the seat at all, so bowl shape is irrelevant. It requires more hand control to use.
Replacing the toilet is worth mentioning honestly. If you have a French curve toilet you dislike anyway, or you’re already planning a bathroom renovation, changing the fixture opens up every seat on the market. It’s the expensive answer, but for anyone doing an aging-in-place retrofit it may be on the list regardless.
Quick reference
| Check | What you want | Where it goes wrong |
|---|---|---|
| Bowl length | ~16.5″ round / ~18.5″ elongated | Landing between the two bands |
| Bolt spacing | 5.5″ standard; most brands accept 5.25″–7.9″ | Older or imported fixtures |
| Bolt-to-tank clearance | 2″+ is safe; 1.5″ is workable | French curve tanks |
| Bolt access from below | Reachable | Skirted toilets — needs top-mount kit |
| Fill valve access | Reachable | Skirted toilets — needs alternate T-valve |
| Outlet (electric seats) | Grounded, GFCI, 15A, within 4 ft | Cord exits the wrong side |
Write your three numbers down before you shop. Every manufacturer publishes their tolerances, and once you know your measurements, checking a spec sheet takes thirty seconds.
Sources for the figures on this page: manufacturer fitment documentation published by TOTO, Bio Bidet, Brondell, Coway and BidetKing, plus NEC bathroom outlet requirements. Tolerances change between product generations — confirm against the spec sheet for the specific model you’re buying. If you have a French curve or wall-hung toilet, contact the retailer with your toilet’s make and model before ordering.