Measure from the bare wall behind the toilet to the centre of its floor bolts, and the room beside it and in front. You get the rough-in to buy (10, 12 or 14″), the bowls that fit with the floor each leaves, and the height to choose.
The toilet that fits
A 12″ rough-in toileta compact elongated bowl: 28¼″ from the wall, 31¾″ clear in front
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Quick answer: measure from the bare wall behind the toilet (not the baseboard) to the centre of the floor bolts. That is the rough-in: 12″ in most homes, 10″ or 14″ in some. Between two sizes, buy the smaller one. Then leave 30″ of floor in front (21″ is the code’s least) and 18″ from the toilet’s centre to anything beside it.
How to use the toilet size finder
- Measure the rough-in: from the finished wall behind the toilet, not the baseboard, to the centre of the bolts that hold it to the floor. With four bolts, use the back two.
- Measure beside it: from the bolts’ centre to the nearest wall, tub or vanity.
- Measure in front: from the wall behind the toilet to the wall, tub or vanity facing it.
- Pick a height: comfort (chair) height or standard. The result shows the rough-in to buy and how much floor each bowl leaves. Copy link keeps the result.
The rules behind the numbers
Rough-in: round down
Toilets are sold for a 10, 12 or 14″ rough-in, and 12″ is the usual one. On Kohler’s spec sheets the tank stands ½–1″ off the finished wall (Santa Rosa ½″, Highline and the 14″ Wellworth ¾″, the 12″ Wellworth 1″). So a toilet made for 12″ still fits a drain at 11½″, but not at 11¼″. Between two sizes, buy the smaller: a 10″ toilet on an 11¼″ drain just stands a little off the wall.
How deep the toilet is
From the finished wall to the front of the bowl, as Kohler draws each model: a round bowl about 28½″, a compact elongated 28¼″, an elongated 30–30½″ on a 12″ rough-in. A compact elongated bowl gives you an elongated seat in a round bowl’s depth. A 10″ rough-in toilet is not much shorter: Kohler’s Highline is 30¼″ on 10″ and 30½″ on 12″.
Floor in front and beside
The NKBA’s bathroom planning guidelines ask for 30″ of clear floor in front of a toilet and 18″ from its centre to a wall or fixture beside it. The building code (IRC R307.1) sets the least: 21″ in front and 15″ to the side.
Height: standard or comfort
A standard bowl’s rim is about 14½″ off the floor (Kohler Wellworth). A Comfort Height bowl (Kohler’s name; others say chair height or right height) is 16½″, “chair-height seating that makes sitting down and standing up easier for most adults” (Kohler). With the seat on, it meets the ADA’s 17–19″ to the top of the seat (§604.4).
Which rough-in to buy
| Drain from the bare wall | Buy a toilet made for |
|---|---|
| 9½ to 11⅜″ | 10″ rough-in |
| 11½ to 13⅜″ | 12″ rough-in |
| 13½″ and more | 14″ rough-in |
Toilet dimensions by bowl
| Bowl | Kohler model read | Rough-in | Wall to front | Rim height | Wall to wall for 30″ in front |
|---|---|---|---|---|---|
| Round | Wellworth K-3577 | 12″ | 28½″ | 14½″ | 58½″ |
| Round | Wellworth K-3947 | 14″ | 30⅜″ | 14½″ | 60⅜″ |
| Compact elongated | Santa Rosa K-3810 | 12″ | 28¼″ | 16½″ | 58¼″ |
| Elongated | Highline K-3889 | 10″ | 30¼″ | 16½″ | 60¼″ |
| Elongated | Highline K-3999 | 12″ | 30½″ | 16½″ | 60½″ |
Wall to front is the sheet’s gap behind the tank plus the toilet’s length. Other makers’ toilets differ by an inch or so: check the one you buy on its own spec sheet.
Three worked examples
A 5′ bathroom, the drain at 12″. Buy a 12″ rough-in toilet. An elongated bowl leaves 29½″ in front, just under the NKBA’s 30; a compact elongated one leaves 31¾″.
An old house, the drain at 11¼″. A 12″ toilet’s tank would hit the wall, so buy a 10″ rough-in. An elongated bowl sits 31½″ out and still leaves 34½″ in front; 16″ to the side meets the code but not the NKBA’s 18.
A powder room, 54″ deep. A 12″ rough-in toilet: an elongated bowl would leave only 23″, so choose a compact elongated one (25¼″ in front). At 15″ to the side it meets the code’s least.
Common toilet sizing mistakes
- Measuring from the baseboard. It takes off its own thickness. Measure from the wall itself.
- Measuring to the wrong bolt. Measure to the centre of the bolts, and with four, to the back pair.
- Rounding up. A 12″ toilet on an 11″ drain will not go back against the wall. Round down.
- Buying elongated for a small room without measuring. It is about 2″ deeper than a round bowl; a compact elongated gives the seat without the depth.
Placing the toilet, vanity and tub together? Try them in the free bathroom layout planner, set the paper holder and grab bars with the bathroom accessory height calculator, and draw the room to scale in the free 2D room planner. Keeping the toilet and changing only the seat? The toilet seat size finder tells round from elongated.
Plan the whole bathroomRead next
- Small bathroom makeovers
- Small powder room ideas
- Small downstairs toilet ideas
- Bathroom remodel ideas
- Basement bathroom designs
Toilet size and rough-in questions
What is a toilet rough-in?
The distance from the finished wall behind the toilet to the centre of its drain, which is where the floor bolts are. Toilets are made for 10, 12 or 14″ rough-ins; 12″ is the usual one.
How do you measure a toilet rough-in?
With the old toilet in place, measure from the bare wall (not the baseboard) to the centre of the floor bolts. With four bolts, measure to the back two. Between two sizes, buy the smaller.
Can I put a 12-inch rough-in toilet on a 10-inch rough-in?
No. The tank would hit the wall: Kohler’s 12″ toilets stand only ½–1″ off it. The other way round works: a 10″ toilet on a 12″ drain just stands 2″ further off the wall.
What are the standard toilet dimensions?
On a 12″ rough-in, about 28½″ from the wall for a round bowl and 30½″ for an elongated one (Kohler Wellworth and Highline), 18–20″ wide. The rim is 14½″ up on a standard bowl and 16½″ on a comfort-height one.
What is a comfort height toilet?
A taller bowl, its rim about 16½″ off the floor instead of 14½″, so it is easier to sit down and stand up. With the seat on, it meets the ADA’s 17–19″. Makers call it comfort, chair or right height.
How much clearance does a toilet need?
The NKBA recommends 30″ of clear floor in front and 18″ from the toilet’s centre to a wall or fixture beside it. The code’s least (IRC R307.1) is 21″ in front and 15″ to the side.
Is a 14-inch rough-in toilet common?
Less than 12″, so the choice is smaller, but the major makers sell them (Kohler’s Wellworth K-3947, for one). 14″ is the largest of the three standard sizes: past it, a 14″ toilet simply stands further off the wall.