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Do bidet attachments fit all toilets?

Almost all, not all. A bidet attachment fits most standard two-piece toilets in the US, because it slides under the seat you already have and uses the same two seat bolts. The toilets that cause trouble are one-piece toilets with a curved slope where the bowl meets the tank, wall-hung and tankless toilets, and some skirted toilets where the water pipe is hidden.

You can know before you buy. It takes three measurements, one look at the water pipe behind the toilet, and about five minutes with a tape measure. This page walks you through all of it, with the numbers.

The short answer, by toilet type

Find your toilet in this table first. Then measure, because "usually" is not the same as "yours".

The three measurements that decide it

Lift the seat and the lid. Grab a tape measure. These are the three numbers that every maker's fit guide comes back to.

1. Bolt spacing: the distance between the two seat bolts

Measure from the center of one seat bolt to the center of the other. In the US the standard is about 5.5 inches (140 mm). Attachments use slotted plates, so most of them take a range around that. One retailer's fitment guide gives 5 to 7.5 inches as the range its non-electric attachments accept.

If your bolts are much closer or much wider than that, you probably have an imported or older toilet, and you need to check the attachment's range before buying.

2. Tank gap: from the bolts to the tank

Measure from the center of a seat bolt straight back to the front face of the tank. The attachment's body sits in that strip. The same fitment guide asks for at least 1.5 inches. Less than that, and the attachment hits the tank, or pushes the seat so far forward that it no longer lines up with the bowl.

This is the number most people skip and the one that most often decides "doesn't fit". It also catches the French-curve problem: if the surface behind the bolts isn't flat for that 1.5 inches, the plate rocks.

3. Bowl length: round or elongated

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

• Round: about 16 to 17.5 inches.
• Elongated: about 18 inches or more (18.5 is common).

Most attachments fit both, because the seat, not the attachment, has to match the bowl. A few models need an elongated bowl because the nozzle reaches further forward. If the product page names a bowl shape, believe it.

More on long bowls in our guide to a bidet that fits an elongated toilet. If the area behind your bolts curves up into the tank, read bidet for a French curve toilet, and Kohler owners can check their model in bidet to fit a Kohler toilet.

Write the four numbers down or take a photo of the tape in place. If you ever have to ask a seller "will it fit", those photos answer it in one message.

The part people forget: the water side

A non-electric attachment runs on the same cold water that fills your tank. It connects with a T-shaped adapter that sits between the tank and the supply hose. So the fit question has a second half: can the T-adapter go in?

Find your tank inlet

Look under the left side of the tank. You'll see a valve coming out of the wall or floor (the shut-off), a hose or pipe going up, and a plastic or metal nut where it meets the bottom of the tank. That nut is the tank inlet. On US toilets it is a standard 7/8 inch thread, which is why US bidet kits ship with a 7/8 inch T-adapter.

Flexible hose or rigid pipe?

If the line from the wall to the tank is a flexible braided hose, you're fine: it unscrews from the tank and screws onto the bottom of the T. If it is a rigid chrome or copper pipe, the T-adapter adds about an inch of height, so the rigid pipe won't reach anymore. The fix is cheap and normal: replace that pipe with a flexible braided supply line from a hardware store. Measure the old one so you buy the right length.

If the T won't thread on or there's no room for it under the tank, our page on a bidet T-valve that doesn't fit goes through each cause.

Is the shut-off valve working?

Turn the wall valve clockwise. If it won't move, or it still lets water through, sort that first. You need to shut the water off to put the T-adapter in. A stuck valve is the one point in this whole job where some people call a plumber.

Skirted toilets

On a skirted toilet the inlet may be hidden behind the side panel, or the supply comes out of the wall low and to the side. The seat side of the attachment usually fits fine. For the water, you may need a longer bidet hose, or a T that goes on the wall valve instead of the tank. Some brands sell a skirted kit. Check where your water comes in before you buy.

Outside the US

The UK, Europe and Australia use different thread sizes at the wall valve, so the US 7/8 inch T-adapter won't fit there. A kit for those countries uses a different tee. If you're not in the US, the "will it fit" answer depends on which kit is in the box.

Your seat matters too

The attachment sits between the bowl and the seat. The seat's hinges bolt through the attachment's plates. So the seat has to cooperate.

• Standard bolt-down seats (bolts with nuts underneath the rim): the easiest case.
• Top-fix seats (bolts you tighten from above, common on one-piece toilets): they still work, but the expanding anchors have to grip through the attachment's plate. Make sure the bolts are long enough.
• Quick-release and soft-close seats: these clip onto a hinge bracket. Most attachments work with them, because the bracket bolts through the plate like any seat. Check that the seat still clicks on fully once the plate is underneath.
• Seats with built-in nightlights, or heated seats: they work the same way, but they're thicker, so check the gap at the back.

The seat will sit a few millimeters higher at the back, by the thickness of the plates. Many attachments come with spacers or bumpers so the seat doesn't rock. If your seat wobbles after install, the bumpers are the first thing to adjust.

Signs it won't fit (before you buy)

• The space behind the bolts slopes up into the tank with no flat ledge.
• There's less than about 1.5 inches from the bolts to the tank.
• No tank, or a metal flush pipe instead of a tank.
• The bolt spacing is far off 5.5 inches.
• The water line comes up through the floor right under the tank with no room for a T.
• The toilet is in an RV or boat, or it's a compact model for small bathrooms.

None of these is a judgment on your toilet. They just mean you need a different kind of bidet: a handheld sprayer on the wall, a full bidet seat made for your shape, or a travel bottle.

What to do if it doesn't fit

The short version is below; for every symptom and its part, see bidet attachment doesn't fit.

If you've already bought one and it doesn't sit right, work through this before sending it back:

1. Slide it back or forward. The plate slots let the attachment move. It should sit as far back as it goes without touching the tank, with the nozzle over the bowl, not over the rim.
2. Check it's square. The nozzle points straight forward, center of the bowl. A crooked attachment pushes the seat crooked.
3. Adjust the bumpers or spacers under the seat so the seat sits level and stops rocking.
4. Hose won't reach: buy a longer braided hose with the same fittings (often 3/8 inch on both ends). Don't stretch the short one.
5. Rigid pipe won't reach the T: swap it for a flexible supply line, as above.
6. It really doesn't fit: put the original parts back (you kept the seat bolts and the old supply line, right?), pack it up, and use the return window. Most sellers state a window, and it's usually counted from delivery, so don't sit on it.

Rentals: will it fit my lease?

An attachment doesn't drill or cut anything. It uses the seat bolts and screws onto the tank inlet, and it comes off the same way. That's why renters choose attachments. Keep the original supply line and seat hardware in a bag under the sink. When you move out, put them back, and the toilet is exactly as it was. Your lease is yours to read; some say you need permission for any plumbing change, even a reversible one.

A five-minute fit check you can do now

1. Lift the seat. Measure bolt to bolt. Write it down.
2. Measure from a bolt back to the tank. Look: is it flat?
3. Measure from between the bolts to the front of the rim.
4. Look under the tank, left side. Flexible hose or rigid pipe? Is there a valve on the wall, and does it turn?
5. Take two photos: one from above with the seat up, one of the water pipe.

That's all a seller needs to tell you yes or no. When ours goes on sale, we will tell you before you pay if your toilet is the weird one. Meanwhile you can find out which bathroom god you are with the ASSJET quiz, which works on every toilet.

Once you know it fits, the next question is the install. Our step-by-step on how to install a bidet attachment covers the T-adapter, the hose and the leak check. Still on the fence about the whole idea? Read whether bidet attachments are worth it.

FAQ

Do bidet attachments fit round toilets?

Yes, most do. The seat has to match the bowl shape, not the attachment. A few models need an elongated bowl, and their product page says so.

Do bidet attachments fit one-piece toilets?

Many do, if there's a flat area of about 1.5 inches behind the seat bolts. One-piece toilets with a smooth slope into the tank (a French curve) usually don't.

Can a bidet be installed on any toilet?

No. Wall-hung, tankless and flush-valve toilets, plus RV and compact toilets, are the usual exceptions. For those, a wall-mounted handheld sprayer or a seat built for that model is the answer.

Do I need a plumber to check if it fits?

No. A tape measure and a look under the tank tell you. The only time a plumber helps is when the wall shut-off valve is stuck.

Will an attachment fit with my soft-close seat?

Usually. Soft-close seats bolt their hinge bracket through the attachment's plates like any seat. Check the seat clicks back on fully after the plate is in.

Does it fit outside the US?

The attachment itself might, but the water connection differs. UK, European and Australian toilets need a different tee from the US 7/8 inch one.

Not sure yet? Take the bathroom god quiz first. It's eight questions, and it doesn't ask for measurements. More answers in our guides.

Sources

1. Will a Bidet Fit My Toilet? Check in 60 Seconds, Bio Bidet. https://biobidet.com/blogs/news/will-a-bidet-fit-my-toilet
2. Non-Electric Bidet Attachment Fitment Guide, BidetKing. https://bidetking.com/non-electric-bidet-attachment-fitment-guide
3. Can You Install a Bidet On Any Toilet?, Premier Bidets. https://premierbidets.com/blogs/news/can-you-install-a-bidet-on-any-toilet
4. How to Install a Bidet, TUSHY (skirted and flushometer notes). https://hellotushy.com/blogs/bidets/how-to-install-a-bidet