A replacement toilet seat that is even slightly the wrong size will wobble, overhang the rim or leave part of the bowl exposed. The good news is that getting it right takes a tape measure and about two minutes. Here is exactly what to measure, and the mistakes to avoid.
What you need
- A tape measure or a ruler
- Your phone, to take a photo from above
- Something to note the numbers down
The three measurements that matter
Always measure the toilet pan (the bowl), not your old seat. If the old seat never fitted properly, copying it will only repeat the problem.
1. Length
Measure from the centre of the two fixing holes at the back of the pan to the outer front edge of the rim. This tells you whether you need a shorter, rounder seat or a longer, oval one.
2. Width
Measure across the widest part of the rim, from outer edge to outer edge. A seat that is too narrow leaves the rim exposed. One that is too wide hangs over the sides.
3. Distance between the fixing holes
Measure from the centre of one fixing hole to the centre of the other. Many universal hinges can be adjusted to suit different spacings, but not all of them, so this number is worth having.
Check the shape
Toilet pans come in a few common shapes. Look at your pan from directly above:
- Round or standard: a shorter, circular bowl, common in compact bathrooms.
- Oval or elongated: longer from back to front, with a more egg-shaped outline.
- D-shaped: a straight back edge with a rounded front, often on modern designs.
- Square or designer shapes: usually need a seat made for that specific model.
A clear photo taken from directly above the pan, with the seat lifted, is often enough for us to confirm the shape.
Top fix or bottom fix?
Look at how the hinges are fastened. With bottom fixing, the nuts are tightened from underneath the pan. With top fixing, everything is tightened from above, which is common on back-to-wall and wall-hung toilets where there is no access underneath. Choosing a seat with the wrong fixing type is one of the most common reasons a replacement will not fit.
Common mistakes to avoid
- Measuring the old seat instead of the pan.
- Measuring from the back of the pan rather than from the centre of the fixing holes.
- Ignoring the fixing type (top fix versus bottom fix).
- Guessing the shape from memory instead of checking from above.
Not sure? Send us the numbers
Once you have the length, width and fixing hole distance, send them with a photo through our Find My Spare form. We will match them to the right seat, whether that is the original part or a compatible alternative. If you still need to work out which model you have, read our guide on how to identify your toilet seat model.
Not sure what you need?
Share a photo or details and our team will help you find the right spare.