There are really only 2 sizes you need to concern yourself with: “round” or “elonglated”. Generally, it is easy to tell just by looking whether you have a round or elongated shaped toilet. If you prefer to measure, just to be sure, then measure from the front of the bowl to the middle of the screws at the back of the bowl/lid area. Here are the standard toilet bowl sizes:
- Round Toilet Bowl: 16.5 inches
- Elongated Toilet Bowl: 18.5 inches
What does vary is the width of the bowl from side to side. But it’s usually not enough to worry about, as most standard size toilet seats and lids will cover most toilet bowls, even if they’re slightly narrower or even wider than the next one.