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Sizing up a new toilet seat is not as easy as it seems. Today, there are many different toilet seat sizes, and several different toilet sizes to pair them with.

This handy guide helps you cut through the maze of toilet seat sizing issues and get the right seat for your new or existing toilet.

Figuring Out Standard Toilet Seat Sizes

The standard toilet seat size is based on the type of toilet you own. There are two types of toilets: elongated and round. The round toilet is bulbous in shape and shorter from front to back. The elongated toilet has a thinner profile but is longer from front to back. Each requires a different size toilet seat, as one will not fit on the other properly.

Most toilet seats manufactured today fit one of the two major toilet bowl sizes, because all manufacturers generally build their toilet bowls to one of the two measurements. However, some toilet bowls have different shapes and require specific types of seats.  So, before your replace a toilet seat, take some time to measure your toilet bowl first. This way you can easily make a comparison to the toilet seats you see in the store, before you buy.

Rounded and Elongated Toilet Seat Sizes

The elongated toilet seat measures 18.5 inches from the mounting holes to the front edge of the toilet seat. Rounded toilet seats measure 16.5 inches from the mounting nuts to the front edge of the toilet seat. The difference is a mere two inches, but it is significant. Elongated toilet seats don’t fit on round toilets and vice versa.

Elongated Toilet Seats = 18.5 inches long

Rounded Toilet Seats = 16.5 inches long

Toilet Seat Widths

Most toilets are the same width.

Commercial and Small Toilet Seat Sizes

You will find smaller toilet seats used in commercial buildings, restaurants and restrooms that measure 15.8 inches from front to back or smaller. Other toilets are even smaller than this. RV and boat toilets, or outhouse toilet seats measure as small as 12 to 13 inches long.

Measuring a Toilet Seat

Measuring a toilet set is fairly straight forward but there are several measurements to take. The first is the length from the mounting holes to the front of the toilet seat, the next is the overall length from front edge to back edge (not to the mounting holes), the inner width and outer width of the seat.

Measure across the toilet at the widest point to get the inner and outer seat width, then measure from front edge to mounting nuts, and to the back edge of the seat. The outer seat width must be wider than your bowl, but the inner seat width smaller than the inner bowl width. The length from the mounting nuts on the toilet to the front edge of the toilet bowl is always smaller than the length on the toilet seat.