Toilet Seat Size, Round vs Elongated: How to Measure the Bowl, Which Seat Fits Kohler, TOTO and American Standard, and How to Replace It
Measure two things: 5 1/2 inches between bolt-hole centres, then midpoint to front rim. About 16 1/2 inches is round, about 18 1/2 inches is elongated (Bemis).
- Verified
- Updated
- 7 min read
- 13 sources
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Short answer
A toilet seat is matched by two tape measurements, not by the toilet brand. Bemis’s measuring guide puts the standard distance between the centres of the two mounting holes at 5 1/2 inches; hook the tape at the midpoint, about 2 3/4 inches from either hole, and measure to the outside edge of the front rim. About 16 1/2 inches is a round bowl and about 18 1/2 inches is elongated, and Bemis says a round seat will not fit an elongated bowl, nor the reverse. Kohler’s seat guide draws the same line from the seat side: a round-front seat measures 16 3/4 inches or less from the hinge bolt to the front, an elongated seat 18 5/8 inches or more, and Kohler says the elongated seat also fits compact elongated toilets. Bemis’s size guide adds that its seats fit Kohler, American Standard, Crane and the other leading makers’ bowls, so the length picks the seat and the bolt hardware only decides how it goes on.
The picks
Bowl measures about 16 1/2 in from bolt midpoint to front rim
Mayfair by Bemis Linden Slow Close Seat, Round (843SLOW)
toiletseats.com: 16.75 in deep, 14.375 in wide, 5.5 in bolt spread, Top-Tite fastening installs from the top, Whisper-Close hinge, fits all manufacturers' round bowls
Bowl measures about 18 1/2 in, including compact elongated per Kohler
Mayfair by Bemis Linden Slow Close Seat, Elongated (1843SLOW)
toiletseats.com: 18.688 in deep, 14.125 in wide, 5.5 in bolt spread, Top-Tite fastening installs from the top, Whisper-Close hinge, fits Kohler, American Standard and TOTO elongated bowls
Round bowl, and you want the seat to lift off for cleaning
Kohler Cachet ReadyLatch Round Seat, K-4639
Kohler install guide 1035808 for K-4636/K-4639: quick-release hinge, lift the covers and pull the seat forward; bolts and nuts tightened from below
If the old seat is the only thing you measured, you may be copying the last owner’s mistake: measure the bowl, and for a Washlet or bidet seat use the bidet fit page instead.
How do you measure a toilet bowl for a seat?
The mounting holes are the two holes at the back of the bowl rim that the seat hinges bolt through; every figure below is measured from them.
| Measurement | How to take it | Round | Elongated | Source |
|---|---|---|---|---|
| Bolt-hole spacing | Centre of one hole to centre of the other | 5 1/2 in | 5 1/2 in | Bemis measuring guide |
| Bowl length | Tape hooked at the midpoint between the holes (about 2 3/4 in from either) to the outside edge of the front rim | About 16 1/2 in | About 18 1/2 in | Bemis measuring guide and both Bemis size guide PDFs |
| Seat length, if measuring the old seat | Hinge bolt to the front of the seat | 16 3/4 in or less | 18 5/8 in or more | Kohler seat guide |
| Width | No maker guide opened prints a bowl-width step; Mayfair’s seats list 14.125 to 14.375 in wide | 14.375 in (Linden round) | 14.125 in (Linden elongated), 14.25 in (Cameron) | Mayfair product pages |
The bolt spacing is the same on both shapes, so a wrong-shape seat bolts on and then overhangs or falls 2 inches short. Only the length to the rim differs.
Which seat fits which bowl?
| Bowl | What the makers print | Seat to buy | Where it says so |
|---|---|---|---|
| Round | Bemis: about 16 1/2 in to the rim. Kohler: seat 16 3/4 in or less | A round seat; Bemis says an elongated seat will not fit | Bemis measuring guide, Kohler seat guide |
| Elongated | Bemis: about 18 1/2 in. Kohler: seat 18 5/8 in or more | An elongated seat; Bemis says a round seat will not fit | Bemis measuring guide, Kohler seat guide |
| Compact elongated | Kohler: its elongated seat fits elongated and compact elongated toilets. No maker page opened prints a compact length in inches | An elongated seat whose maker says it fits; measure first | Kohler seat guide |
| Either | Mayfair One Fit: fits round and elongated bowls, 19.48 in deep | The One Fit, if you cannot measure before buying | Mayfair One Fit page |
The makers’ thresholds are a class, not one exact length: Bemis prints about 16 1/2 and 18 1/2 inches for the bowl, Kohler 16 3/4 and 18 5/8 inches for the seat, and the Mayfair Linden seats measure 16.75 and 18.688 inches deep. A bowl between the two classes gets measured twice, then the elongated seat Kohler says covers compact elongated.
Brand-specific seats: Bemis’s size guide says its seats fit Kohler, American Standard, Crane and other leading manufacturers’ bowls, and the Linden elongated page names Kohler, American Standard and TOTO. No page opened this session names a standard toilet that refuses an aftermarket seat, but kohler.com and American Standard’s knowledge base would not load, so that is a gap. A skirted or one-piece bowl is decided by the hardware table instead.
Which hinge and hardware do you need?
Hardware matters when you cannot reach under the bowl or want the seat off for cleaning.
| Hardware | How it fastens | When it is the answer | Maker document |
|---|---|---|---|
| Bottom-fix bolt and nut | Bolt drops through the bowl hole, nut tightened from underneath | Any bowl you can reach under | Kohler guide 1035808 (K-4636, K-4639); TOTO manual 0GU036-1 (plastic bolts and nuts) |
| Top-mount anchor | Anchor sits in the bowl hole, screw tightened from above | Skirted or one-piece bowl with no access underneath | TOTO manual 0GU543 (SS124, flathead screwdriver only); Kohler Hyten guide (Grip-Tight); Mayfair Linden Top-Tite |
| Pre-installed metal nuts | Bolts thread into nuts already in the toilet | Toilets that ship with the nuts fitted | Kohler instructions 17676T |
| Quick-release | Lift the hinge covers and pull the seat forward, hardware stays on the bowl | Seat comes off for cleaning | Kohler guide 1035808; Kohler Hyten guide (Quick-Release button) |
TOTO ships both systems across seat generations: the 2006 manual 0GU036-1 uses two plastic bolts and nuts under the bowl, while the SS124 manual 0GU543 uses two anchors, two lock washers, two round washers, two screws and two bracket covers, all fitted from above.
How do you replace a toilet seat?
Condensed from Kohler’s guide 1035808 and TOTO’s manual 0GU543. TOTO needs only a flathead screwdriver; Kohler adds an adjustable wrench.
- Remove the old seat and its hardware, and lift the hinge covers on the new seat.
- Bottom-fix: drop the two bolts through the hinge holes and bowl holes, then thread a nut on each from underneath. Top-mount: seat the anchors in the bowl holes without pushing them through, then centre the hinge holes over them.
- Check the seat sits square and, on the TOTO, covers the bowl with a slight overhang.
- Tighten with the screwdriver, and the wrench on the Kohler nuts, until the seat is immobile. Both makers say not to overtighten.
- Close the hinge covers, then raise the lid and let it drop: Kohler’s 17676T sheet says it should close slowly.
How often does a seat need replacing?
None of the maker documents opened prints a replacement interval. The trigger is a cracked hinge, a seat that will not stay tight, or the wrong shape. The same tape measure that sizes a fill valve sizes the seat.
Measure the bowl, then buy one seat
The Mayfair Linden round and the Linden elongated are one family in two lengths, 16.75 and 18.688 inches deep, with Top-Tite hardware fitted from above. The flaw: the Linden is a wood-core seat whose maker page makes no quick-release claim. If you want the seat to lift off for cleaning, the Kohler Cachet K-4639 is the round seat whose install guide documents it, and it fastens from below. Skip all three if the bowl is elongated and you want quick-release: the elongated Cachet showed no buyable offer on 30 September 2026, and the best toilet seat comparison carries that shortlist.
Frequently asked questions
Will a round toilet seat fit an elongated toilet?
Bemis says no in plain words: a round seat will not fit an elongated bowl, and an elongated seat will not fit a round bowl. The bolt holes are the same 5 1/2 inches apart on both, which is why a wrong seat bolts on and then overhangs or falls short by about 2 inches at the front. Measure the bowl length before ordering.
What size seat does a compact elongated toilet take?
Kohler's seat guide says its elongated seat, 18 5/8 inches or more from hinge bolt to front, fits elongated and compact elongated toilets. No maker page opened this session prints a compact elongated bowl length in inches, so measure from the midpoint between the bolt holes to the front rim and buy the seat whose maker says it fits that length.
How far apart are toilet seat bolts?
Bemis's measuring guide gives 5 1/2 inches between the centres of the two mounting holes as the standard, with the midpoint about 2 3/4 inches from each. Every Mayfair by Bemis seat page opened this session lists a 5.5 inch bolt spread, round or elongated, so the spacing does not tell you the bowl shape; only the length to the front rim does.
How do I fit a seat on a skirted toilet where I cannot reach underneath?
Use top-mount hardware. TOTO's SoftClose manual 0GU543 installs the SS124 with anchors that drop into the bowl holes and screws tightened from above with a flathead screwdriver. Kohler's Hyten reference guide shows Grip-Tight anchors tightened from above the same way. The Mayfair Linden's Top-Tite fastening also installs from the top, per its toiletseats.com page.
Do TOTO and Kohler toilets need their own brand of seat?
Not on the evidence the makers publish for standard seats. Bemis's size guide says its seats fit Kohler, American Standard, Crane and other leading manufacturers' bowls, and the Mayfair Linden elongated page names Kohler, American Standard and TOTO. A Washlet or bidet seat is a different question, covered on the bidet fit page. kohler.com and American Standard's pages could not be opened this session.
Fact sheet and how to cite this page
- Answer
- Bemis’s measuring guide: the standard spacing between the mounting-hole centres is 5 1/2 inches; from the midpoint between the holes to the outside front rim, a round bowl measures about 16 1/2 inches and an elongated bowl about 18 1/2 inches. Kohler’s seat guide draws the line on the seat itself: round-front 16 3/4 inches or less, elongated 18 5/8 inches or more, and the elongated seat also fits compact elongated toilets.
- Applies to
- Mayfair by Bemis Linden 843SLOW 000, round, 16.75 in deep, 14.375 in wide, 5.5 in bolt spread
- Mayfair by Bemis Linden 1843SLOW 000, elongated, 18.688 in deep, 14.125 in wide, 5.5 in bolt spread
- Mayfair by Bemis Cameron 1841EC 006, elongated, 18.813 in deep, 14.25 in wide, 5.5 in bolt spread
- Mayfair by Bemis One Fit universal, round or elongated, 19.48 in deep, 14.28 in wide, 5.5 in bolt spread
- Kohler Cachet K-4639 (Kohler install guide 1035808, quick-release hinge)
- TOTO SoftClose SS124 (TOTO manual 0GU543, top-mount anchors)
- Compatibility basis
- Bemis’s How to Measure a Toilet Seat article and its two seat size guide PDFs, Kohler’s Toilet Seats Guide (bowl shapes), the Mayfair by Bemis product pages on toiletseats.com, Kohler’s seat installation guides (1035808, 17676T and the Hyten reference guide) and TOTO’s SoftClose installation manuals 0GU543 and 0GU036-1
- Assumptions
- No maker page opened this session prints a compact elongated bowl length in inches; Kohler only says its elongated seat fits elongated and compact elongated toilets, so this page prints no compact number.
- No maker sizing guide opened prints a bowl-width measuring step; the width figures here are the seat widths on the Mayfair product pages, 14.125 to 14.375 inches.
- kohler.com refused every request this session (access denied and timeouts); the Kohler sizing figures come from Kohler’s Asia Pacific site, and the Kohler installation PDFs are Thailand-market and China-market documents.
- American Standard’s knowledge base returned an empty page shell, so this page carries no American Standard seat statement.
- The claim that a standard body fixes the 5 1/2 inch spacing appeared only in a search snippet and was not opened, so no standard number is cited; Bemis’s own wording, the standard, is what the page repeats.
- Method
- Bolt spacing, bowl lengths, seat thresholds and seat dimensions copied from each maker’s own guide, PDF or product page; installation steps condensed from Kohler’s and TOTO’s installation sheets. OwnerSpec measured no bowl and installed no seat.
- Primary source
- Bemis / toiletseats.com, How to Measure a Toilet Seat: 5 1/2 in between hole centres, midpoint about 2 3/4 in, round about 16 1/2 in, elongated about 18 1/2 in (manufacturer or vendor document)
- Facts verified
- Last updated
- Cite as
- OwnerSpec, "Toilet Seat Size, Round vs Elongated: How to Measure the Bowl, Which Seat Fits Kohler, TOTO and American Standard, and How to Replace It", https://ownerspec.com/plumbing/parts/toilet-seat-size-round-vs-elongated/, facts verified 30 September 2026.
Every figure above also appears, with its source, in the article. All sources ยท How OwnerSpec verifies numbers
Sources
- Bemis / toiletseats.com, How to Measure a Toilet Seat: 5 1/2 in between hole centres, midpoint about 2 3/4 in, round about 16 1/2 in, elongated about 18 1/2 in (manufacturer or vendor document)
- Bemis, Toilet Size Guide (PDF, 2020): round 16.5 in, elongated 18.5 in, measured between the holes to the front of the bowl (manufacturer or vendor document)
- Bemis, Toilet Seat Size Guide (PDF, 2010): round typically 16.5 in, elongated typically 18.5 in; Bemis seats fit Kohler, American Standard, Crane and other leading manufacturers' bowls (retailer listing or retailer-hosted document)
- Kohler Asia Pacific, Toilet Seats Guide, Bowl Shapes: elongated seat 18 5/8 in or more, fits elongated and compact elongated toilets; round-front seat 16 3/4 in or less (manufacturer or vendor document)
- Kohler, toilet seat installation guide for K-4636, K-4639, K-4713 and K-4732 (PDF 1035808): install steps and quick-release hinge (manufacturer or vendor document)
- Kohler, Quiet-Close seats with quick-release installation instructions (PDF 17676T): plastic-nut and pre-installed metal-nut hardware, drop the lid to test the slow close (manufacturer or vendor document)
- Kohler, Hyten Elevated Toilet Seat Install Reference Guide (PDF): Grip-Tight anchors tightened from above, Quick-Release button (manufacturer or vendor document)
- TOTO, SoftClose Toilet Seat SS124 installation manual (PDF 0GU543): top-mount anchors, lock washers, screws, bracket covers, flathead screwdriver (manufacturer or vendor document)
- TOTO, SoftClose Toilet Seat installation manual (PDF 0GU036-1, 2006): plastic bolts and nuts tightened under the bowl (manufacturer or vendor document)
- Mayfair by Bemis, Linden round enameled wood seat 843SLOW 000 (toiletseats.com): 5.5 in bolt spread, 16.75 in depth, 14.375 in width, Top-Tite, Whisper-Close (manufacturer or vendor document)
- Mayfair by Bemis, Linden elongated enameled wood seat 1843SLOW 000 (toiletseats.com): 5.5 in bolt spread, 18.688 in depth, 14.125 in width, fits Kohler, American Standard, TOTO (manufacturer or vendor document)
- Mayfair by Bemis, Cameron elongated seat 1841EC 006 (toiletseats.com): 5.5 in bolt spread, 18.813 in depth, 14.25 in width (manufacturer or vendor document)
- Mayfair by Bemis, One Fit universal plastic seat (toiletseats.com): fits round and elongated bowls, 5.5 in bolt spread, 19.48 in depth, 14.28 in width (manufacturer or vendor document)