Toilet seats look generic and are not. Order the wrong shape and it will overhang the bowl or leave a gap at the front, and either way it will not sit properly. The good news is that three measurements settle it completely, and you already own the tape measure.
The Two Shapes
Almost every domestic toilet takes one of two seat shapes, matching the bowl beneath it:
- Round — roughly circular, about 16.5 inches from the seat bolts to the front edge.
- Elongated — oval, about 18 to 18.5 inches over the same span.
These are not interchangeable. An elongated seat on a round bowl overhangs badly; a round seat on an elongated bowl leaves the front of the bowl exposed. If you are not sure which bowl you have, our comparison of elongated versus round bowls explains the difference in more detail.
The Three Measurements
Take all three before ordering. It takes less time than reading this page.
1. Bowl length
Measure from the centre point between the two seat bolts at the back, straight forward to the outside front edge of the bowl. Around 16.5 inches means round. Around 18.5 inches means elongated. Anything in between is worth measuring again — some compact elongated bowls land near 17.5 inches and take an elongated seat.
2. Bolt spread
Measure centre to centre between the two seat bolt holes. On the overwhelming majority of toilets this is 5.5 inches, and it has been standard for decades. If yours is different, you have an unusual or older fixture and will need to match it specifically.
3. Bowl width
Measure across the bowl at its widest point. Most bowls are close to 14 to 14.5 inches. This matters less than the other two, but it is worth checking if you are buying a seat with a wide or contoured lid, or a bidet seat with side controls.
Why This Matters More for Bidet and Heated Seats
A basic seat is inexpensive and easy to return. A bidet seat, heated seat or soft-close model is neither. These also frequently need clearance behind the bowl for a control housing and a connection to the water supply, so check the manufacturer’s required rear clearance as well as the shape.
If you are considering one, our toilet seat reviews list shape compatibility for each model, and the Brondell Swash review covers what to expect from an elongated bidet seat specifically.
Materials, Briefly
Once the size is settled, material is mostly preference:
- Plastic (polypropylene) — light, cheap, easy to clean, the default.
- Moulded wood — heavier and warmer to sit on, but the finish can chip or swell over time in a humid bathroom.
- Enamelled or solid wood — handsome, expensive, and the most demanding to keep looking good.
Soft-close hinges are worth the small premium in most households, particularly with children. Quick-release hinges, which let you lift the seat off without tools, make cleaning around the bolts far less irritating.
If the Old Seat Will Not Come Off
Corroded seat bolts are common on older toilets. Penetrating oil and patience solve most of them. Plastic bolts can often be cut through with a hacksaw blade, working carefully to avoid scratching the porcelain. Metal bolts may need a nut splitter. Do not lever against the ceramic — a cracked bowl turns a fifteen-pound job into a replacement toilet.
A Note on Height
Seat thickness varies by an inch or so between models, which is enough to notice if you are near the edge of comfortable. If you are trying to raise the seating position, a thicker seat is a partial solution but a proper comfort height toilet is the better one.
The Short Version
Measure bowl length to identify shape, confirm the bolt spread is 5.5 inches, and check the width if the seat is anything more elaborate than basic. Order to match. It is one of the few bathroom jobs where getting it right first time is genuinely easy.
