Take three measurements before you shop for a new toilet

You need three numbers: the rough-in distance (how far the bolts are from the wall), the bowl shape, and the seat height. Most toilets come in one rough-in size, one bowl shape, and one height, so getting these wrong means the new toilet will not fit or will sit at the wrong angle. Measure twice, write the numbers down, and bring them with you or use them when ordering online.

The rough-in is the measurement that matters most. It is the distance from the wall behind the toilet to the center of the bolts that hold the toilet to the floor. Standard rough-in is 12 inches, but older homes sometimes have 10-inch or 14-inch rough-ins. If you install a toilet with the wrong rough-in, it will either stick out too far into the bathroom or sit too close to the wall, and you cannot fix it without moving the drain pipe.

Key Takeaways

  • Measure the rough-in distance from the wall to the center of the floor bolts; standard is 12 inches, but 10-inch and 14-inch rough-ins exist in older homes.
  • Check whether your bowl is round or elongated by measuring the distance from the seat hinge to the front of the bowl; round bowls are typically 16 to 17 inches, elongated bowls are 18 to 19 inches.
  • Note the seat height of your current toilet; standard height is 15 to 17 inches, and comfort height (also called chair height) is 17 to 19 inches.
  • Write down all three measurements and bring them when you shop, or use them to check the product specifications before you order online.

How to measure rough-in distance

Turn off the water and flush the toilet to empty the tank. Use a tape measure to find the distance from the wall directly behind the toilet to the center of one of the two bolts on the floor. Measure to the center of the bolt, not the edge. If the wall has baseboard trim, measure from the wall surface itself, not from the trim.

Write down the number. If it is close to 12 inches (within half an inch), your rough-in is standard. If it is closer to 10 inches or 14 inches, that is your rough-in size. Do not round up or down; if you measure 11.5 inches, that is a 10-inch rough-in, not a 12-inch.

How to measure bowl shape

Bowl shape is either round or elongated. Measure from the back of the seat hinge (the part bolted to the bowl) to the front edge of the bowl. Round bowls measure 16 to 17 inches. Elongated bowls measure 18 to 19 inches. If your measurement falls between the two, you have an elongated bowl; manufacturers size them to fit standard elongated seats.

Bowl shape matters because a round bowl takes up less floor space, while an elongated bowl is more comfortable for most people. If you replace a round bowl with an elongated one, it will stick out further into the bathroom. If you replace an elongated bowl with a round one, you will lose legroom.

How to measure seat height

Measure from the floor to the top of the seat (not the lid). Standard height is 15 to 17 inches. Comfort height, also called chair height, is 17 to 19 inches. Comfort height toilets are easier to sit on and stand up from, especially for older adults or people with mobility issues, but they take up slightly more visual space in the bathroom.

If your current toilet is standard height and you want to switch to comfort height, you can do that — the rough-in and bowl shape do not change. Just make sure the new toilet is labeled as comfort height or chair height before you buy it.

What to do with your measurements

Write all three numbers on a piece of paper or take a photo of your notes. When you shop in a store, show the measurements to a sales associate and ask them to confirm that the toilet you are looking at matches all three. Most big-box home improvement stores have toilet displays where you can sit on different models to feel the height difference.

If you are ordering online, open the product page and look for a specifications section. The rough-in, bowl shape, and seat height should all be listed. Cross-check each one against your measurements before you add the toilet to your cart. If the specifications do not list all three, contact the seller and ask.

Common measurement mistakes

The most common error is measuring from the baseboard instead of the wall. Baseboard trim can be half an inch thick or more, which throws off your rough-in measurement. Always measure from the wall surface itself. If the wall is uneven, measure from the closest point to the toilet.

Another mistake is confusing the bowl shape with the seat shape. Some seats are round even though the bowl is elongated, or vice versa. Measure the bowl itself, not the seat. If you are unsure, look at the toilet from above — a round bowl is nearly circular, and an elongated bowl is noticeably longer front to back.

A third mistake is assuming all toilets of the same brand or model are the same height. Manufacturers make both standard and comfort height versions of the same toilet line. Always check the product label or specifications to confirm the height.

When measurements do not match standard sizes

If your rough-in is not 10, 12, or 14 inches, or if your bowl is between round and elongated, you may have an unusual toilet. Take a photo of the toilet from above and from the side, and bring those photos to the store or send them to the online seller. A sales associate can help you figure out what size you actually have.

If your rough-in truly does not match any standard size, you have two options: hire a plumber to move the drain pipe (expensive), or look for a toilet with an offset flange, which can adjust the rough-in by a couple of inches. Offset flanges are less common and cost more, but they avoid the need for plumbing work.

Frequently Asked Questions

Can I install a toilet with a different rough-in than my current one?

No, not without moving the drain pipe. The rough-in must match the location of the drain hole in your floor. If you install a toilet with the wrong rough-in, it will either sit too far from the wall or too close, and the bolts will not line up with the floor holes. A plumber can relocate the drain, but that costs several hundred dollars.

What if I measure my rough-in and it is 11 inches?

An 11-inch measurement is a 10-inch rough-in. Manufacturers round down, so anything from 9.5 to 10.5 inches is considered a 10-inch rough-in. Order a toilet labeled as 10-inch rough-in, not 12-inch.

Do I need to measure the tank or just the bowl?

Measure only the bowl. The tank sits behind the bowl and does not affect the rough-in or bowl shape. Rough-in is measured to the bolts that hold the bowl to the floor, and bowl shape is measured on the bowl itself.

Can I use my old seat on a new toilet?

Only if the new toilet has the same bowl shape. Round seats fit round bowls, and elongated seats fit elongated bowls. If you switch bowl shapes, you will need a new seat. Seats are inexpensive (usually under $50), so it is not a major cost.

What if the store does not have a toilet that matches my measurements?

Ask the sales associate to order one. Most stores can special-order toilets that are not on the floor. If you are ordering online, use the filter options to narrow by rough-in, bowl shape, and height, then check the product specifications before you buy.