How to Measure Toilet Rough-In Before You Buy

01The measurement: bolt center to the wall

The rough-in is the distance from the finished wall behind the toilet to the center of the drain pipe (the closet flange) under the toilet. The simplest way to find it without pulling the toilet is to measure from the wall to the center of the hold-down bolts at the base, the caps you see on each side near the floor. If your toilet has two bolts per side, measure to the rear set, since those sit over the flange.

Measure from the finished wall, not the baseboard or trim, or you will read about a half-inch short. Use a tape held level and straight, and take the reading to the bolt center, not the edge of the bolt. Round to the nearest standard size: a reading near 12 inches is a standard rough-in, around 10 inches is a small rough-in, and around 14 inches is a large rough-in. The number you get is the toilet you can buy.

• ·Measure from the finished wall, not the baseboard or trim
• ·Measure to the center of the rear hold-down bolts, which sit over the flange
• ·~10 inch, ~12 inch, ~14 inch are the three standard rough-ins
• ·12 inch is by far the most common; round your reading to the nearest standard

02Why 10, 12 or 14 inches matters before you buy

Toilets are manufactured for a specific rough-in, and the number is printed on the box and spec sheet. A 12-inch toilet set over a 10-inch rough-in will not have room and the tank will hit the wall; a 12-inch toilet over a 14-inch rough-in will leave an awkward two-inch gap behind the tank. Twelve inches is the overwhelming standard, so most toilets on the shelf assume it, which is exactly why a 10 or 14 inch home catches people out at install time.

Measuring first saves a return trip and a botched install. Older homes (pre-1960s especially) are the usual home of 10-inch rough-ins, while some additions and remodels run 14 inches. If your reading is not close to 12, you are not stuck, but you do need to either buy a toilet rated for your actual rough-in or plan for an offset flange. Knowing the number up front also lets you price the job accurately; our toilet installation cost guide shows how a clean swap compares to one that needs flange or floor work.

03Offset flanges and odd measurements

When your rough-in does not match the toilet you want, an offset flange is the common fix. It is a closet flange whose drain opening is shifted by about an inch from center, letting you move the toilet forward or back to land on a non-standard rough-in without re-plumbing the drain. That can turn an 11-inch reading into a workable 12, for example. Offset flanges are inexpensive parts, but installing one means pulling the toilet and replacing the flange, which is more involved than a simple swap.

If the existing flange is also cracked, corroded or below the finished floor, that is the moment to deal with it, because you already have the toilet off. Flange and wax-ring work has its own cost band, covered in our toilet flange replacement cost guide, and a too-low flange is a leading cause of a toilet that rocks or leaks at the base after install. Once the rough-in and flange are sorted, the choice between a sleek single unit and a traditional tank-and-bowl is the next decision; our one-piece vs two-piece toilet comparison covers which suits your space.