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Bidet that fits an elongated toilet: what to check before you buy

Almost every bidet attachment fits an elongated toilet, and so do most bidet seats sold as "elongated". An attachment slides under the seat you already have, so the bowl's length barely matters to it. A bidet seat replaces your seat, so it has to match the bowl: an elongated seat on an elongated bowl, usually measured at about 18 to 19.5 inches. What really decides the fit is the flat space behind the bolts and the water pipe, not the word "elongated".

Here's how to confirm your bowl is elongated, what each kind of bidet needs, and the elongated toilets that still cause trouble.

Is my toilet elongated or round?

Measure from the center point between the two seat bolts to the front edge of the rim.

Bowl length	Shape	How it looks
About 16 to 17.75 in	Round	Close to a circle. Common in older homes and small bathrooms.
About 18 to 19.5 in (18.5 is common)	Elongated	An oval, longer front to back. Common in newer US homes.
Under 18 in but oval	Compact elongated	Looks elongated, fits the footprint of a round bowl. The tricky one.

Measure, don't guess from looks. A compact elongated bowl looks oval but measures shorter, and some bidet seats made for elongated bowls hang over its front edge.

The three other numbers that matter

"Elongated" only tells you about the front of the bowl. A bidet sits at the back, so these numbers decide more:

Bolt spacing: center of one seat bolt to the center of the other. The US standard is about 5.5 inches. Many seats have adjustable hinges; Signature Hardware's Brookdale elongated bidet seat lists 5-3/8 to 6-7/8 inches.
Tank gap: center of a bolt to the front of the tank. An attachment needs a flat strip of about 1.5 inches here.
Water inlet: under the tank, usually left. A flexible braided hose to the wall valve is the easy case. A rigid pipe needs swapping for a flexible one.

Our guide on whether bidet attachments fit all toilets walks through all four measurements with a table.

Attachment, seat or handheld: what each needs on an elongated bowl

Kind of bidet	Does bowl shape matter?	What to check
Attachment (under your seat)	Barely. Your seat still matches your bowl.	Flat 1.5 in behind the bolts, bolt spacing in its range, the nozzle reaching the middle of the bowl.
Bidet seat (replaces your seat)	Yes. Buy the elongated size for an elongated bowl.	Bowl length in the seat's listed range, hinge spacing, the back shape, an outlet if it's electric.
Handheld sprayer	No.	A place on the wall or tank to hang it, and room for the T-adapter.

Bidet attachments on elongated toilets

An attachment is a thin plate with a nozzle arm that sits between the bowl and the seat. The seat's bolts go through its slots. Because your seat stays, the seat still matches your bowl, round or elongated. That's why most attachments don't name a bowl shape at all, and the ones that do usually say "fits round and elongated".

Two things are worth knowing on an elongated bowl:

Where the spray lands. The nozzle reaches forward from the back of the bowl. On a long elongated bowl, people often sit a little further back than on a round one, which actually helps the aim. If the spray lands too far back, adjust how you sit before you blame the attachment. Your first time using a bidet covers sitting and aiming.
Some models want elongated. A few attachments reach further forward and are made for elongated bowls only. If the product page names a shape, believe it.

For choosing between attachments (one knob or two, one nozzle or two, plastic or metal valve), see how to choose a bidet attachment for your toilet.

Bidet seats on elongated toilets

A bidet seat is a whole new toilet seat with the wash built in. It replaces your seat, so its shape must match the bowl. Sellers list a bowl-length range, and it differs by model even within one brand. Brondell's Swash 1400 lists elongated bowls of 18 to 19.5 inches; its Swash Thinline T44 lists 17.7 to 18.5 inches.

Check the range against your number. If your bowl measures 17.75 inches and the seat starts at 18, the front will overhang.
Check the hinge spacing range against your bolt spacing.
Check the back. Bidet seats have a wide, boxy back where the parts live. On a toilet with little space before the tank, or a curved back, the seat can't slide far enough back.
Electric or not. Electric seats need a grounded outlet near the toilet. Non-electric seats run on cold water like an attachment.

The full trade-off, price to repairs, is in bidet attachment vs seat.

Elongated toilets that still cause trouble

Compact elongated

These have an oval bowl on a short footprint, so they fit small bathrooms. The tank often sits close to the bolts. An attachment may not have its 1.5 inches of flat, and an elongated bidet seat may hang over the front. Measure both.

One-piece with a French curve

Many one-piece elongated toilets have a smooth curve rising into the tank instead of a flat ledge. Neither attachments nor most seats sit on that. Our guide to a bidet for a French curve toilet shows how to tell and what fits.

Skirted elongated

Smooth sides hide the trapway and often the water inlet. The seat side usually fits; the water side may need a longer hose or a T on the wall valve. See the skirted section in our T-valve fit guide.

Comfort height (chair height)

Taller toilets, about the height of a chair. The height doesn't change the fit at all; the bowl and tank are the same shapes. A seat or attachment adds a few millimeters, which nobody notices.

Top-fix seats

Many newer elongated one-piece toilets use bolts you tighten from above. An attachment's plate can stop the rubber anchor gripping. You may need a longer top-fix kit. More in what to do when a bidet attachment doesn't fit.

A five-minute check for an elongated toilet

Measure bolts to the front of the rim. 18 inches or more: elongated.
Measure bolt to bolt.
Measure a bolt to the tank, and check it's flat.
Look under the tank: flexible hose or rigid pipe, and does the wall valve turn?
For an electric seat: is there an outlet within reach of its cord?
Take two photos, from above with the seat up and of the water pipe.

With those numbers you can check any product page in a minute.

Round toilet? Same rules, smaller seat

Attachments fit round bowls just as well, for the same reason: your seat stays. Bidet seats come in a round size too, with their own range. The one thing to watch is a short round bowl with a curved back, where even a round bidet seat can overhang.

Mistakes when buying for an elongated toilet

Buying "elongated" without measuring. Compact elongated bowls catch people out.
Ignoring the tank gap. It's the most common reason an attachment doesn't fit, and the box never mentions it.
Buying an electric seat without an outlet. An extension cord by a toilet isn't a fix.
Keeping the old rigid supply pipe. The T adds height; buy a flexible braided line.
Throwing away the box before the leak check and the first week.

FAQ

Do bidet attachments fit elongated toilets?

Yes, most do. The attachment sits under your existing seat, which already matches your bowl. Check the flat space behind the bolts, not the bowl shape.

How long is an elongated toilet bowl?

About 18 to 19.5 inches, measured from the center between the seat bolts to the front of the rim. 18.5 inches is common. Round bowls are about 16 to 17.75. Brondell's spec sheet uses 18 to 19.5 for elongated and 16 to 17.75 for round.

Can I put an elongated bidet seat on a round toilet?

It'll overhang the front, look odd and may crack under weight. Buy the round size, or an attachment that keeps your round seat.

Do I need a special attachment for an elongated toilet?

Usually no. Most attachments fit both shapes. A few reach further forward and are made for elongated bowls only; their product page says so.

What if my elongated toilet is one-piece?

Check behind the bolts. A flat ledge of about 1.5 inches and an attachment will likely fit. A smooth curve into the tank and it likely won't.

Know your numbers? While we get the first batch ready, take the bathroom god quiz; it fits every bowl shape. More in our guides.

Sources

Brondell Swash 1400 Luxury Electric Bidet Seat for Elongated Toilet, The Home Depot. https://www.homedepot.com/p/Brondell-Swash-1400-Luxury-Electric-Bidet-Seat-for-Elongated-Toilet-in-Biscuit-S1400-EB/302023823
Brondell Swash Thinline T44 Bidet Seat for Elongated Toilets, The Home Depot. https://www.homedepot.com/p/reviews/Brondell-Swash-Thinline-T44-Luxury-Electric-Remote-Controlled-Bidet-Seat-for-Elongated-Toilets-in-White-T44-EW/323289839/1
CL950 spec sheet (fit guideline: elongated 18 to 19.5 in, round 16 to 17.75 in), Brondell. https://www.brondell.com/content/CL950_specsheet_092420.pdf
Brookdale Elongated Bidet Seat (hinge 5-3/8 to 6-7/8 in centers), Signature Hardware via Build.com. https://build.com/signature-hardware-437000/s1995775
Elongated bidet listing, Ace Hardware. https://www.acehardware.com/departments/plumbing/toilets/toilets-and-bidets/4001089
Non-Electric Bidet Attachment Fitment Guide, BidetKing (1.5 in tank gap). https://bidetking.com/non-electric-bidet-attachment-fitment-guide