Last Updated on October 7, 2026
Toilet Seat Size Calculator
Measure your bowl once and find out whether you likely need a round-front, elongated, compact/nonstandard, or bidet-compatible seat.
Products That May Help
These are examples for the common fit categories. Use your result and confirm the product dimensions before ordering.
As an Amazon Associate, BestFlushingToilets.org may earn from qualifying purchases. Verify bowl shape, bolt spacing, mounting style, and product-specific fit requirements before ordering.
Related Guides on BestFlushingToilets.org
Check the full toilet's rough-in, side space, and front clearance before buying a replacement fixture.
If you are replacing the whole toilet, check the rough-in before focusing on bowl or seat shape.
Compare round, elongated, one-piece, two-piece, and other toilet styles if the entire fixture needs replacement.
How to Measure a Toilet Seat Correctly
Remove or lift the old seat so you are measuring the ceramic bowl, not the old seat itself. Start at the centerline of the mounting holes and measure straight forward to the front edge of the bowl.
KOHLER's current toilet-seat buying guide classifies seats measuring 16¾ inches or less as round-front and 18⅝ inches or more as elongated. If your measurement falls between those ranges, do not force it into a category. Compact-elongated, designer, commercial, and proprietary bowls can fall outside simple round/elongated rules.
Bolt spacing is a separate fit check. BEMIS documentation for its 500EC round seat lists 5½-inch hinge spacing, and TOTO's SS113/SS114 round and elongated SOFTCLOSE seats also specify 5½-inch mounting-hole spacing. That makes 5½ inches a useful common reference, but it is not a universal guarantee for every toilet.
For a bidet seat, bowl shape is only the beginning. Rear tank clearance, the seat's adjustable mounting range, nearby power, water-supply access, and the exact toilet contour can all affect fit. TOTO publishes model-specific fit charts for this reason.
Toilet Seat Size FAQ
How do I know if my toilet seat is round or elongated?
Measure from the center of the seat-mounting holes to the front edge of the bowl. KOHLER uses 16¾ inches or less for round-front and 18⅝ inches or more for elongated seat guidance.
What if my measurement is between round and elongated sizes?
Re-measure first. If the number remains between the common ranges, you may have a compact-elongated, designer, commercial, or otherwise nonstandard bowl. Use the toilet model number and the seat manufacturer's exact dimensions.
Is 5½ inches the standard toilet seat bolt spacing?
It is a common U.S. mounting-hole spacing and appears in BEMIS and TOTO examples, but do not assume every toilet uses it. Measure center-to-center and check the seat's adjustment range.
Can I put an elongated seat on a round toilet?
It may physically mount in some cases, but the seat can overhang the bowl and fit poorly. Match the seat to the bowl shape unless the manufacturer specifically says otherwise.
Will any bidet seat fit an elongated toilet?
No. Bidet seats also have rear-clearance, mounting-range, tank-contour, water, and electrical requirements. Always use that bidet model's fit diagram.
What if I cannot reach the underside of the seat bolts?
Your toilet may use concealed or skirted mounting. Look for a seat that supports top-mount hardware or use the exact mounting hardware specified for your toilet.
Official References
- KOHLER — Toilet Seat Buying Guide — round-front and elongated measurement guidance.
- KOHLER — Toilet seat shape reference — 16¾" round-front and 18⅝" elongated examples.
- BEMIS — Product catalog — 500EC round-seat dimensions and 5½" hinge spacing.
- TOTO — SS113 / SS114 SOFTCLOSE seat spec sheet — round and elongated examples with 5½" mounting-hole spacing.
- TOTO — WASHLET C100/C200 fit chart — model-specific rear-clearance guidance.
Hi, I am Jose S. Franz. Currently, I am working as a professional plumber, and our team offers various plumbing services at an affordable price. After my college education, I completed a vocational certification course in plumbing systems and worked with several construction companies. Since then, I have fixed lots of different toilet models, from older to the latest versions. So I have more than 22 years of experience installing plumbing systems and toilets in both residential and commercial buildings.