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Bidet for a French curve toilet: what fits, and what to do instead
Most bidet attachments and most bidet seats don't fit a French curve toilet. The bowl rises in a smooth curve into the tank, so there's no flat ledge behind the seat bolts for a plate to sit on. A few seats with narrow mounting plates are sold for some French curve models, a handheld sprayer always works, and sometimes the cheapest answer is a different toilet.
Here's how to tell in a minute whether yours is one, which toilets are known for it, and every option with what it costs you.
What a French curve toilet is
"French curve" is the name for a shape, not a brand. On most toilets, the flat top of the bowl behind the seat meets the tank at close to a right angle. On a French curve toilet, the tank's front dips in a concave curve that follows the round back of the seat, and the bowl sweeps up into it. There's no corner and no flat strip.
It's almost always a one-piece toilet, where tank and bowl are cast as one. It looks smooth and expensive, and it often has a matching seat with a curved back. Kohler even sells a seat line called French Curve made to follow that shape, and several Kohler one-piece toilets ship with it.
A bidet attachment needs exactly what this shape removes: a flat strip about 1.5 inches deep between the seat bolts and the tank. A bidet seat needs a flat area for its mounting plate and a back narrow enough to slide in. Both fight the curve.
Is yours a French curve? A 60-second check
- Lift the seat and lid. Look at the area between the two seat bolts and the tank.
- Is there a flat shelf? Lay a ruler or a credit card flat behind the bolts. If it lies flat for about 1.5 inches before touching the tank, you have room. If it tips or touches the curve right away, you have a French curve or something close.
- Does the tank's front curve inward? Look from above. A French curve tank front is concave, scooped to follow the seat. A standard tank front is straight.
- Is it one piece? Look for a seam or bolts where the tank meets the bowl. No seam and no tank bolts means one-piece.
- Find the model number. On many toilets it's stamped or printed inside the tank, on the back wall, or under the lid. Write it down: it's the fastest way to check any product's fit list.
Take a photo from above with the seat up, and one from the side. If a seller asks "will it fit", those two photos answer it.
Toilets known for a French curve
These come up again and again on bidet sellers' fit pages. Kohler's own product pages say which ones ship with a French Curve seat.
| Toilet | What's known |
|---|---|
| Kohler Rialto (K-3386, one-piece, round) | Ships with a French Curve seat. One seller says only two bidet seats fit it, and even those overhang the front by about 1.5 inches. |
| Kohler San Raphael (K-3384 elongated, K-3467 round, one-piece) | Ships with a French Curve seat. Some buyers report an attachment working on the elongated one, others say no. Check the exact model. |
| Other one-piece "designer" toilets | Many brands have models with a curved back. The shape, not the brand, decides it. Do the check above. |
If yours is a Kohler, our guide to a bidet that fits a Kohler toilet covers the brand's own fit lists and its models one by one.
Your options, side by side
| Option | Does it fit a French curve? | What it costs you |
|---|---|---|
| Standard bidet attachment | Usually no. The plate rocks on the curve. | A return, if you already bought one. |
| Attachment with a long or trimmable arm | Sometimes. One seller says a model whose arm you can cut shorter is the only attachment that can fit some French curve toilets. Buyers disagree by model. | Cutting it ends the return; try the fit before you cut. |
| Bidet seat with a narrow mounting plate | Some fit some models. Sellers name a few that go on certain French curve toilets. | A seat is often several times the price of an attachment, many need an outlet, and fit is model by model. |
| Handheld sprayer on the wall | Yes. It doesn't touch the seat at all. | You aim it by hand, and the hose stays under pressure (see attachment vs handheld sprayer). |
| Replace the toilet with a two-piece | Then anything fits. | One seller puts a new two-piece elongated toilet under $200, about $250 to $300 with a plumber. |
| Travel or bottle bidet | Yes, nothing to mount. | Fill it every time. Fine to try the idea, not for every day. |
Option 1: an attachment, carefully
An attachment is the cheapest bidet there is, so it's worth knowing when it might still work on a curved toilet.
- Some "French curve" toilets have a short flat strip. If the ruler test gives you even an inch of flat before the curve, and the attachment's body is slim, it may sit. Try it before tightening anything.
- The plate must lie flat. Press each corner with the seat off. Any rock means it will loosen every time someone sits.
- Don't stack spacers under the plate to fake a flat surface. The bolts end up too short, and the seat sits high and crooked.
- Don't cut anything until you've tried the fit. A trimmed arm can't go back.
- Mind the water side. One-piece toilets often have the tank inlet low and close to the wall valve, with little room for the T-adapter. Our T-valve fit guide covers that.
If it rocks, it doesn't fit. Our guide on what to do when a bidet attachment doesn't fit covers putting everything back and returning it.
Option 2: a bidet seat made for the shape
Some bidet seats have a smaller, rounded back and a narrow mounting plate, so they slide further back than most. Sellers list a few that fit certain French curve toilets. Three things to know before buying one:
- Fit is model by model. A seat that fits a Rialto may not fit a San Raphael. Find the toilet's model number and look for it on the seat's fit list, or send the seller your photos.
- Round vs elongated still matters. On a round, short bowl, even a seat that fits can hang over the front edge. One seller measured about 1.5 inches of overhang on a Rialto.
- Most of these are electric. They need a grounded outlet near the toilet. No outlet means an electrician first. Our comparison of bidet attachment vs seat covers outlets, price and what breaks.
Option 3: a handheld sprayer
A handheld sprayer mounts on the wall or the tank side and connects to the same water line with a T-adapter. It never touches the seat, so the bowl's shape doesn't matter. It's the most reliable "it fits" answer for a French curve toilet.
The trade-off is real: you hold it and aim it, you need a free hand, and the hose is under water pressure all the time unless you close the valve after each use. Some people prefer it. Others try it and miss the hands-free spray.
Option 4: a different toilet
It sounds drastic, but on paper it can be cheaper than a specialist seat. A standard two-piece elongated toilet takes nearly every attachment and seat. One bidet seller estimates under $200 for the toilet and about $250 to $300 with a plumber's labor.
It makes sense when the toilet is old, already needs work, or you want an electric seat and it doesn't fit any. It doesn't make sense in a rental: the toilet isn't yours to swap.
Renters with a French curve toilet
You can't change the toilet and you may not want to drill. Your realistic choices are a handheld sprayer that hooks onto the tank side instead of screwing into the wall, or a bottle bidet. Keep the original supply line in a bag under the sink if you add a T-adapter, so you can put it back when you leave. Our guide to installing a bidet in an apartment covers the lease side.
How to ask a seller "will it fit"
Send this, and you'll get a real answer instead of "fits most toilets":
- The toilet's brand and model number.
- Bolt spacing (center to center).
- Distance from a bolt to the tank, and how much of it is flat.
- Bowl length from between the bolts to the front of the rim.
- One photo from above with the seat up, one from the side.
When ours goes on sale, we'll ask for exactly this and tell you before you pay. We'd rather lose a sale than ship you something that rocks.
Mistakes people make with curved toilets
- Trusting "fits most toilets" on the box. Most toilets aren't French curve toilets.
- Buying by bowl shape alone. Elongated or round doesn't tell you whether the back is flat.
- Over-tightening the bolts to stop a rock. That cracks plastic plates and bolts, and on porcelain can chip the bolt hole.
- Waiting too long to return. Return windows usually start at delivery.
FAQ
Can you put a bidet on a French curve toilet?
Sometimes. Most attachments won't sit flat. A few bidet seats with narrow plates fit some models, and a handheld sprayer fits all of them.
How do I know if my toilet has a French curve?
Lift the seat. If the bowl curves up into a scooped tank front with no flat ledge behind the bolts, it's a French curve.
Are all one-piece toilets French curve?
No. Many one-piece toilets have a flat area behind the seat and take an attachment fine. Check for the flat strip, not the number of pieces.
Do Kohler French Curve seats work with a bidet attachment?
The seat isn't the problem; the bowl under it is. If the toilet behind the bolts is curved, the attachment's plate has nothing flat to sit on, whatever seat goes on top.
Will spacers make an attachment fit?
Not under the plate. Spacers and bumpers level the seat on the rim. They can't make a curved surface flat, and stacking them under the plate makes the bolts too short.
Not sure what shape you've got? Measure with our guide to whether bidet attachments fit all toilets. Or take the bathroom god quiz, which works on any toilet. More in our guides.
Sources
- What Bidet Toilet Seats Will Fit My Kohler Rialto Toilet?, BidetKing. https://bidetking.com/blog/what-bidet-toilet-seats-will-fit-my-kohler-rialto-toilet/
- Best Bidets for French Curve Toilets, Many Bidets. https://www.manybidets.com/bidet-seats-for-toilets-with-a-french-curve/
- Rialto one-piece round-front toilet with French Curve toilet seat (K-3386), Kohler. https://www.kohler.com/en/products/toilets/shop-toilets/rialto-one-piece-round-front-1-6-gpf-toilet-with-rim-jet-flush-technology-left-hand-trip-lever-and-french-curve-toilet-seat-3386
- San Raphael one-piece round-front toilet with French Curve toilet seat (K-3467), Kohler. https://www.kohler.com/en/products/toilets/shop-toilets/san-raphael-one-piece-round-front-1-6-gpf-toilet-with-ingenium-flush-technology-left-hand-trip-lever-concealed-trapway-and-french-curve-toilet-seat-3467
- Non-Electric Bidet Attachment Fitment Guide, BidetKing. https://bidetking.com/non-electric-bidet-attachment-fitment-guide