Order a toilet online, unbox it, and discover it sits four inches off the wall — or worse, won't bolt down at all. The culprit is almost always the rough-in: the one measurement people skip because they've never heard of it. It takes thirty seconds with a tape measure and it's the difference between an easy install and a return shipment.
What "rough-in" means
The rough-in is the distance from the finished wall behind the toilet to the centre of the drain pipe in the floor (the closet flange). Toilets are engineered around three standard distances: 12 inches (the modern standard), 10 inches (common in older homes and condos where the stack sits close to the wall), and the rarer 14 inches.
How to measure it — 30 seconds
- With the old toilet still installed, find the closet bolts — the two caps at the base holding the toilet down.
- Measure from the wall (not the baseboard — hold the tape above it) straight to the centre of a closet bolt.
- Read the number: ~11½–12½" means a 12" rough-in; ~9½–10½" means 10"; ~13½"+ means 14". If your toilet has four bolts, measure to the rear pair.
Measuring for a brand-new bathroom instead? Measure from the finished-wall surface (account for drywall if it's not up yet) to the centre of the flange.
Why it matters when you buy
A 12" toilet on a 10" rough-in physically won't fit — the tank hits the wall before the outlet reaches the drain. A 10" toilet on a 12" rough-in installs, but leaves an awkward gap behind the tank. Manufacturers publish the rough-in for every model, and it's the first spec we list — see how to find it in our guide to reading plumbing spec sheets.
If your rough-in is 10 inches
Don't panic: the selection is smaller but strong. TOTO's Drake family offers dedicated 10" tank/bowl combinations, Kohler and American Standard both make 10" versions of their best-sellers, and skirted models often hide the difference elegantly. Browse the toilets collection and check each product's specification sheet for the rough-in — or ask us and we'll shortlist 10" models for you.
Special cases worth knowing
- Wall-hung toilets ignore floor rough-in entirely — the drain goes into the wall through an in-wall carrier tank. They're the escape hatch for truly awkward plumbing (and free up floor space) — see wall-hung options.
- Rear-outlet (back-spud) toilets also drain through the wall — measure the outlet height instead.
- Corner installs and offset flanges exist for renovation edge cases; an offset flange can convert 10" to 12" but restricts flow — treat it as a last resort, not a plan.
Frequently asked questions
My measurement is 11 inches — which do I buy?
Measure again to the bolt centre, above the baseboard. True 11" readings usually mean a 10" rough-in with thick wall finishes; a 10" toilet is the safe choice, and a 12" will not fit.
Does rough-in affect the seat or comfort?
No — it only positions the toilet relative to the wall. Height and bowl shape are separate choices; see our chair-height vs standard guide.
Is the rough-in the same for bidet-seat toilets?
Yes. WASHLET+ and standard versions of the same model share the same rough-in.