Measure the bowl from the middle of the seat's two bolt holes to the front edge of the rim. You get the seat that fits, round or elongated, a check on the bolt holes, and the seat that brings it to a comfortable height.
Seat to buy
An elongated toilet seatyour bowl 18½″, an elongated one 18½″ · bolt holes 5½″ apart, the standard
As an Amazon Associate I earn from qualifying purchases. This post contains affiliate links. If you buy through them we may earn a commission at no extra cost to you.
Product prices and availability are accurate as of the date and time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply to the purchase of this product. Certain content that appears on this site comes from Amazon. This content is provided "as is" and is subject to change or removal at any time.
Shop round toilet seats
As an Amazon Associate, Dreamy Home Style earns from qualifying purchases.
Shop elongated toilet seats
As an Amazon Associate, Dreamy Home Style earns from qualifying purchases.
Quick answer: measure from the midpoint between the seat’s two bolt holes to the front edge of the rim. About 16½″ is a round bowl, about 18½″ an elongated one (Bemis, the seat maker), and one will not fit the other. The bolt holes are 5½″ apart on a standard US toilet, so any seat of the right shape fits them.
How to use the toilet seat size finder
- Lift the seat off, or measure around it, and find the two bolt holes at the back of the bowl.
- Measure from the midpoint between them (2¾″ in from either hole) straight to the front edge of the rim, outside edge.
- Say how the bowl looks from above, an oval or nearly a circle: it settles a measurement in the middle.
- Measure between the holes, centre to centre, to check the hinges, and the rim’s height off the floor if you want the seat’s height checked too.
- Read the seat to buy. Copy link keeps the result.
The rules behind the numbers
Two shapes, two lengths
Bemis, the largest seat maker, in its own measuring guide: “Place the hook of your tape measure at the midpoint and measure to the outside edge of the toilet bowl rim in front. A round toilet bowl will measure approximately 16 ½″ in length, while an elongated bowl is approximately 18 ½″.” And: “A round toilet seat absolutely won’t fit an elongated bowl, and … the opposite is also true.”
The bolt holes
Bemis: “The standard measurement for this distance is 5 ½″, with a midpoint of approximately 2 ¾″”. Every Kohler toilet sheet we read prints the same “Seat-mounting holes: 5-1/2″”, round and elongated alike.
Compact elongated bowls
A compact elongated toilet is built to fit a round bowl’s space, but its bowl is elongated: Kohler’s Santa Rosa sheet recommends its elongated seats. Buy elongated.
The seat’s height
The ADA puts the top of the seat 17–19″ above the floor (2010 Standards, §604.4). Kohler’s standard rims are 14½″ and its Comfort Height rims 16½″, so a seat ½–2½″ thick brings a Comfort Height bowl into that band and a standard bowl needs 2½–4½″. Give the rim’s height and the finder works it out.
How the finder decides
It names the nearer shape, up to 1″ either side of 16½″ and 18½″. Less than ¼″ either side of the middle, 17½″, it asks how the bowl looks, and an oval or a round look settles it; more than 1″ outside both sizes, it is not a standard US bowl.
Toilet seat sizes
| Your measurement | The bowl | The seat |
|---|---|---|
| 15½–17¼″ | round (about 16½″) | round |
| 17¼–17¾″ | between the two | look at the shape |
| 17¾–19½″ | elongated (about 18½″) | elongated |
| under 15½ or over 19½″ | not a standard US bowl | ask the toilet’s maker |
Measured from the midpoint of the bolt holes to the outside of the rim in front. The holes: 5½″ apart.
Three worked examples
16⅝″ from the holes. A round seat: ⅛″ from Bemis’s 16½″.
18¾″ from the holes. An elongated seat, a compact elongated bowl included.
17½″, right between. Most likely elongated, but look: an elongated bowl is an oval, a round one nearly a circle, and the model number inside the tank lid settles it.
Common toilet seat mistakes
- Measuring from the tank. Start at the midpoint between the bolt holes, not at the tank or the wall.
- Measuring the old seat. A seat can overhang or fall short of the rim; measure the bowl.
- Buying round for a compact elongated toilet. Its bowl is elongated, even though the toilet is short.
- Guessing by eye. Two inches decide it, and a seat of the wrong shape overhangs or leaves the rim bare.
Replacing the whole toilet? The free toilet size and rough-in finder measures the drain and the room around it. The bathroom accessory height calculator places the paper holder beside it, and the free 2D room planner lays out the bathroom.
Size the toiletRead next
Toilet seat size questions
What are the toilet seat sizes?
Two: round, for a bowl about 16½″ from the bolt holes to the front, and elongated, for one about 18½″ (Bemis). The bolt holes are 5½″ apart on both.
How do I measure a toilet seat?
Measure the bowl, not the seat: from the midpoint between the two bolt holes to the outside edge of the rim in front. About 16½″ is round, about 18½″ elongated.
Round vs elongated toilet seat: what is the difference?
About 2″ of length. An elongated seat is roomier to sit on; a round one suits a small bathroom. They are not interchangeable: each fits only its own bowl.
What are elongated toilet seat dimensions?
About 18½″ from the middle of the bolt holes to the front, with the holes 5½″ apart (Bemis).
Are toilet seats universal?
Within a shape, mostly: US seats share the 5½″ bolt spacing. Across shapes, no: a round seat does not fit an elongated bowl, or the other way round.
How high should a toilet seat be?
17–19″ from the floor to the top of the seat, for an accessible toilet (ADA §604.4). On a 16½″ Comfort Height rim a seat ½–2½″ thick gets there; a standard 14½″ rim needs 2½–4½″.
Does a compact elongated toilet take a round or elongated seat?
Elongated. The toilet is short front to back, but its bowl is elongated: Kohler recommends its elongated seats for its compact elongated Santa Rosa.