Per North American plumbing standards, all toilets are either round or elongated (AKA oval or oblong).
Measure your toilet, not your toilet seat to determine if you need a round or elongated toilet seat. NOTE: Measure from the seat mounting holes to the front, top edge of the bowl (see diagram link below).
- Elongated bowls = 18.5 inches
- Round bowls = 16.5 inches
To select round or elongated on the product page, please scroll down to locate the SIZE field, and click it -- the drop down feature allows you to select round or elongated.