How to Measure a Toilet Seat (and Find the Right Type)

Buying a seat that does not match your bowl is the easiest mistake to make — and the easiest to avoid. You only need a tape measure and two minutes to get it right. This guide shows exactly what to measure, what the numbers mean, and how to narrow down the type of seat that suits your bathroom.

What you need

  • A tape measure (a flexible sewing tape is easiest around the rim)
  • Your toilet’s brand and model number, if you can find it (usually stamped inside the tank or on the back of the bowl)
  • About two minutes

If you are replacing an existing seat, take it off first or measure with the lid up so you can see the bolt holes clearly.

The three measurements

How to measure a toilet bowl for a new seat Top-down diagrams of a round and an elongated bowl. Length is measured from the centre of the seat bolt holes to the front rim: about 16.5 inches for round and 18.5 inches for elongated. Bolt holes are usually 5.5 inches apart. Width is measured across the widest outside edge. Round 5.5″ ≈16.5″ Elongated 5.5″ ≈18.5″
  1. Bowl length: measure from the centre point between the two seat bolt holes to the outside front edge of the rim. About 16.5″ means round; about 18.5″ means elongated.
  2. Bowl width: measure across the widest outside edge of the rim (usually around 14″).
  3. Bolt spacing: measure centre-to-centre between the bolt holes. Most US toilets use 5.5″.

One-piece, wall-hung and many European or designer toilets use non-standard shapes. Always check the seat maker’s compatibility list for your exact toilet model.

1. Bowl length

Measure from the midpoint between the two seat bolt holes to the outside front edge of the rim. This is the measurement that tells you the shape:

  • About 16½ inches — a round bowl. Common in older homes and small bathrooms.
  • About 18½ inches — an elongated bowl. Common in newer homes and “comfort height” toilets.

2. Bowl width

Measure across the widest point of the outside rim. Most residential bowls are around 14 inches wide. Width matters most for seats with built-in electronics, such as bidet seats, because their side panels or bases can overhang a narrow bowl.

3. Bolt-hole spacing

Measure from the centre of one bolt hole to the centre of the other. Most US toilets use 5½ inches. If yours differs, check that the seat’s hinges are adjustable before you buy.

Extra checks for bidet and heated seats

  • Power: electric bidet seats and plug-in heated seats need a grounded outlet near the toilet, ideally GFCI-protected. Measure the distance to the outlet and compare it with the seat’s cord length.
  • Tank clearance: bidet seats have a control unit at the back. Measure from the bolt holes to the tank, because some one-piece toilets leave too little room.
  • Water connection: bidet seats connect to the toilet’s water supply with a T-valve. Check that the shut-off valve behind the toilet works before installation.

Find the right type of seat

Answer four quick questions for a starting recommendation. It runs in your browser and does not store your answers.

1. What shape is your toilet bowl?
2. Is there a power outlet within about 4 ft of the toilet?
3. What matters most?
4. Budget

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