Updated September 28, 2026
How to Measure Your Toilet Rough-In (and the Mistake Almost Everyone Makes)
The rough-in is the one number that decides which toilets fit your bathroom. It takes 60 seconds to measure, and the most common mistake adds half an inch you don't have.
What rough-in means
It's the distance from the wall behind your toilet to the center of the drain, which is where the two floor bolts sit. Toilets come in three: 12 inches (most homes), 10 inches (tight or older bathrooms) and 14 inches (some older homes).
How to measure it
- Pop the caps off the two bolts at the base of your toilet.
- Hook your tape on the finished wall (drywall, tile) behind the toilet, above the baseboard.
- Measure to the center of either bolt.
The mistake almost everyone makes
Measuring from the baseboard. A half-inch baseboard makes a true 12-inch rough-in read 11.5, and people go hunting for a toilet size they don't need. If you get something between 11.5 and 12.5, you have a standard 12-inch rough-in.
Two more measurements that matter
Round or elongated
Measure from the seat bolt holes to the front edge of the bowl. About 16.5 inches is round; about 18.5 inches is elongated. Elongated bowls are about 2 inches longer, so check the door swing and walking room before switching from round.
Clearance
Most codes want at least 15 inches from the toilet's centerline to a side wall or fixture, and about 21 inches of open space in front. Older bathrooms are sometimes tighter than that, which is worth knowing before you size up.
What we do
All three toilets we install are 12-inch rough-in, chair height, elongated. Not sure what you have? We call before install day to confirm it, so nobody shows up with a toilet that doesn't fit.
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