Bidet–toilet compatibility: the complete fit procedure

The checker

Enter your measurements — A (bolt-line centre to front rim), bolt spread, and the flat deck clearance between the bolt holes and the tank — and tell it your toilet's architecture. It applies the same rules this page documents, including the per-model floor: most seats need 1.5″ of bolt-to-tank clearance; the Swash 1400 needs 1.75″.

Fit by brand and line

Brand is a weak predictor — every maker below ships both perfectly standard bowls and at least one architecture that fights a seat. What follows is the desk's orientation per line; your measurements remain the verdict.

TOTO

The deepest fit documentation in the industry, because TOTO sells both sides of the joint. Standard two-piece lines (Drake and its kin) take any seat in the correct size. The proprietary case is WASHLET+: designated seats whose water and power connections hide inside matching TOTO bowls. A WASHLET+ seat is specified for its paired bowls — treat the pairing list as a requirement, not a suggestion — while TOTO's non-plus seats fit other brands' standard bowls normally. Skirted TOTO lines (the Aquia class and one-piece designs) follow the skirted procedure below.

Kohler

The ecosystem player: Kohler publishes a seat-by-toilet compatibility grid for its PureWash and Novita families across Archer, Cimarron, Highline, Memoirs and the rest — the practice this desk wishes were universal (see the Kohler brand file). Outside the grid, standard Kohler two-piece bowls fit standard seats. The known fights: the one-piece design lines with curved rear decks — San Raphael and Rialto are the names that recur on exclusion lists, including Alpha's — and skirted Comfort Height models, which take the top-mount procedure.

American Standard

Mainstream lines (Cadet, Champion, Studio) are conventionally shaped and seat-friendly in both sizes. The brand's own bidet seats are specified against its bowls, but third-party fit follows the standard rules; the compact and right-height variants still answer to Measurement A, not to their marketing names.

Gerber

Trade-grade and builder-grade lines (Viper, Avalanche classes) are dimensionally conventional — Gerber's professional installed base means standard bolt spreads and decks — and are among the least surprising bowls a seat shopper can own. Verify A and the tank clearance as usual; surprises are rare.

Glacier Bay

The budget big-box line, and the class where variance lives: bowls are sourced and revised more freely than the trade brands', so a model name guarantees less. Measure the actual fixture in your bathroom — never the listing — and pay particular attention to the bolt-to-tank deck, which runs short on some compact Glacier Bay designs. Attachments, which forgive more, are the lower-risk class here.

The three architectures that change the procedure

Skirted and one-piece toilets: the top-mount procedure

Both architectures hide the underside of the seat-bolt holes — the skirt conceals the trapway and bolt access; the one-piece casting integrates the tank so there is no gap to reach through. The standard fix is top-mount hardware: expanding rubber-sleeve anchors that drop into the bolt holes from above and grip as the bolt tightens. Many seat makers include or sell the kit; the procedure is: confirm the kit matches your seat's bracket, seat the anchors fully before the bracket goes on, and budget an extra half hour over a standard install. If a maker's fit materials say your specific one-piece is excluded even with the kit, that is a different and stronger statement — believe it.

French curve toilets: the exclusion-list case

A small family of design bowls curves the rear deck upward into the tank, exactly where a seat's bracket and housing need a flat landing. Some seats physically cannot mount; others mount and sit wrong. Manufacturers publish exclusion lists for these models, and French curve is the one architecture where the desk's advice is simply to obey them: if your bowl is listed, the answer is an attachment that tolerates the geometry (some do), a different seat the maker certifies, or no bidet seat. Do not improvise hardware against a curve.

The compact-elongated case

Compact elongated bowls — Measurement A around 17.5″, between the standard classes — are elongated in shape on a shortened footprint. The elongated seat size is the correct purchase (a round seat will perch and look wrong), but two checks tighten: the seat's rear housing may crowd the tank on the shortened deck, making the clearance measurement decisive, and the sittable length shrinks, which matters for larger users. When A lands in the gap, buy elongated, verify the retailer's fit checker against your exact toilet model, and keep the return window in mind.

The pre-purchase checklist (the no-JS procedure)

• Measurement A: 18–19″ → elongated seat. 16–17″ → round. ~17.5″ → compact elongated: elongated seat, extra checks above.
• Bolt spread: 5.5″ is standard. Substantially different → non-standard fixture; stop and consult the seat maker's fit line before ordering.
• Bolt-to-tank clearance: 1.5″ minimum for most seats and attachments; 1.75″ for the Swash 1400. Below the floor → the bracket cannot sit flat; this is the commonest real-world misfit.
• Architecture: two-piece with exposed bolts → standard install. One-piece or skirted → top-mount kit required, confirmed for your seat. French curve → check the maker's exclusion list and obey it. Wall-hung → professional territory; bring measurements to the manufacturer first.
• Side room: side-arm control seats need a hand's width beside the bowl; tight water closets take remote models.
• Outlet (electric): GFCI within ~4 ft of the toilet, on the correct side for the cord. No outlet → the cost ledger prices the electrician, or the non-electric classes take the purchase.
• Supply: a working shutoff valve at the toilet — the universal tee point. A valve that won't close is a plumber-first problem, not a bidet problem.

Fit is the only bidet question that cannot be argued with after purchase. Ten minutes with a tape measure is the whole discipline; everything else in this category is taste.

Frequently asked questions

My toilet is a Kohler. Which seats fit?

Start with Kohler's own compatibility grid for PureWash and Novita — it is the most complete brand-published fit data in the category. For third-party seats, standard Kohler two-piece bowls follow the standard rules; the recurring exclusions are the curved-deck one-piece designs (San Raphael, Rialto class) and they appear on other makers' lists too.

What is WASHLET+, and can I use the seat on another brand?

WASHLET+ seats are built to pair with specific TOTO bowls, routing water and power connections invisibly through the fixture. The pairing is the product: fit one only to a listed bowl. TOTO's standard (non-plus) seats fit any brand's bowl that passes the measurements.

The Swash 1400 needs 1.75″ — what if I have 1.6″?

Then the Swash 1400 is not your seat, though most rivals are: the general floor is 1.5″ of flat deck. Per-model requirements like the 1400's exist because bracket geometry differs — which is why this guide prints floors per model rather than one universal number.

Do attachments fit toilets that seats can't?

Often, yes. An attachment occupies only the bolt line and the bowl's underside, forgives bowl-length mismatches, and clears some decks that defeat a seat bracket. It is not a universal solvent — the bolt spread and minimum deck still apply — but for compact, budget-brand and odd-geometry bowls it is the lower-risk class, as the Glacier Bay note above reflects.

My measurement A is 17.5 inches. What do I buy?

An elongated seat — you have a compact elongated bowl. Then verify clearance with extra care, since the shortened deck is exactly where rear housings crowd tanks, and confirm against the retailer's model-specific fit checker before the return window becomes relevant.