How do I measure a toilet rough-in before buying one?

The rough-in is the distance from the wall behind the toilet to the center of the drain. You can't see the drain with a toilet in place, but the floor bolts line up with it, so you measure to them.

1. 1Find the bolts. Pop off the caps at the base of the toilet on each side. Under them are the bolts that hold the toilet to the floor.
2. 2Measure from the wall, not the baseboard. Hook the tape on the finished wall behind the toilet, above the baseboard, and measure to the center of one bolt. American Standard puts the typical number this way: "Most toilets bolt to the floor 12-inches from the wall (not counting the baseboard)."
3. 3Write it down before you shop, along with the brand and model of the old toilet if you can find it.

If the old toilet is already out, measure from the finished wall to the center of the drain opening in the floor instead.

### What if the number isn't 12 inches?

Then you likely have a 10- or 14-inch rough-in, and you'll need a toilet made for it. Most toilets are built for 12 inches, and the options narrow at other sizes. Manufacturers list the rough-in on every spec sheet. Kohler's K-4302 spec sheet, for example, lists a 10-inch or 12-inch rough-in. Its K-6355 spec sheet lists a standard 12-inch rough-in only, and says that model can't be combined with the K-5383 or K-5381 for use in 10-inch or 14-inch installations. So read the spec sheet for the exact model, not just the product name.

A 12-inch toilet on a 14-inch rough-in will leave a gap behind the tank. A 12-inch toilet on a 10-inch rough-in won't fit against the wall.

### Why the baseboard still matters

Some spec sheets measure the other way. Kohler's K-6355 sheet says the rough-in must be 12 inches or more from the base of the wall or baseboard. If you have a thick baseboard, or tile that steps out at the bottom of the wall, measure to that too. A tank that fits against the wall can still hit the trim.

Rough-in is the must-have. These are the checks that save a return trip.

### Space around the toilet

Code sets minimum clearances. Phoenix's adopted plumbing code says a water closet "shall not be set closer than 15 inches (381 mm) from its center to any side wall, partition, vanity or other obstruction." It also requires "not less than a 21-inch (533 mm) clearance in front of a water closet" to any wall, fixture or door. A new toilet that sticks out farther than the old one can eat into that front clearance, especially in a small half bath. See toilet clearance code for the full rules.

### Bowl shape

American Standard says to "check the tank height, bowl shape and rough-in dimension of your available space." Round-front bowls are more compact. Elongated bowls extend farther and add comfort. If the room is tight, measure from the front of the old bowl to the nearest obstruction before choosing an elongated model.

### Seat height

Taller "comfort" or "chair" height bowls are common now. American Standard says the traditional rim height is about 15 inches from the floor and that its Right Height or Chair Height toilets have a rim height of 16-1/2 inches. For the full comparison, see comfort height vs standard toilets.

### Where the water supply valve sits

Skirted toilets, the ones with smooth sides that hide the trapway, can clash with an existing supply valve. Kohler's K-6355 sheet says the existing supply stop may need to be relocated if it's less than 8-1/2 inches from the centerline of the toilet. It suggests you "Dry fit the toilet to confirm if the supply stop needs to be relocated." It also notes the supplied hose will extend roughly 6 inches from the toilet, and that a longer supply hose may be used if it doesn't reach.

Check this before you fall for a model. Phoenix's adopted plumbing code caps how much water a toilet can use. Its main table, Table 604.4(1), lists a maximum of 1.28 gallons per flushing cycle for a water closet. A second table allows 1.6 gallons, but the code applies it only to specific buildings it lists, such as tall buildings and certain care facilities. For a typical home, 1.28 is the number to look for on the spec sheet.

The spec sheet is also where the flush rate, bowl shape, rough-in and seat height all appear together. Read it once, and compare it to the numbers you wrote down.

Sometimes, but it's a bigger job than swapping a toilet. The rough-in is set by where the drain comes up through the floor. Changing it means moving the drain, which means opening the floor. Kohler's K-6355 sheet tells installers to install or relocate the supply and outlet as needed to match its rough-in dimensions. For new construction, it says to install a new supply stop following the dimensions in its diagram.

That makes sense during a remodel, when the floor is already open. For a simple replacement, it's usually easier to buy a toilet made for the rough-in you have.

A sound flange, or an approved seal. Phoenix's adopted plumbing code says connections between the drain and floor-outlet fixtures "shall be made with a floor flange or a waste connector and sealing gasket." The flange also has minimum thicknesses by material, such as 0.25 inch for plastic.

When the old toilet comes up, look at the flange before setting the new one. A cracked or loose flange is easier to fix with the floor open. See how to fix a broken toilet flange.

### Quick checklist

Picked your toilet? If the rough-in is odd or the flange is bad, we can handle the install. HQ is licensed and insured, and every estimate is free with upfront pricing.