Home Saddle width calculator
Free tool
Saddle width calculator
Measure your sit bones once, pick how you ride, and get a saddle width range in millimeters and inches — plus what the same number means for the chair you sit on the rest of the day.
Your number, your position
Sit on corrugated cardboard on a hard bench for about thirty seconds, stand up, and measure between the centers of the two dents. Enter the number and pick its unit — inches, centimeters or millimeters.
The end points of these bands are published by the fitting guides below — nothing added when you are fully extended, about +20 mm for a typical mountain-bike position, up to 4 cm sitting upright. The steps between them are our reading of those guides, not anyone’s standard. Brands fold their own corrections into size charts and saddle shapes differ, so treat the result as the width to try first, not a verdict. The percentile line compares your number with the upright measurements of 45 men and 45 women in a 2021 study — a rough placement, not a ranking.
Bike shop, club or clinic? Print the one-page sit-bone measuring card (PDF) and hand it out — the method, the allowance table and the sources, free to distribute.
Put this calculator on your own site
Bike shops, clubs and fit blogs are welcome to embed it. Copy the snippet as it is — the credit line below the frame is a normal link on your page (everything inside an iframe belongs to us, so it is the only part search engines can see), and nothing else is needed.
The rules behind the number
A saddle has to be wider than the bones it carries, and how much wider depends on how far forward you rotate. The published figures, and where we read between them:
| Position | Added to sit-bone width | Why |
|---|---|---|
| Fully extended (time trial, triathlon) | about 0 mm | The pelvis is rotated so far forward that the contact points sit closer together than the cardboard measured; saddle width matches sit-bone width |
| Sporty (road, on the hoods) | +10 to +20 mm | Some forward rotation; a common fitter example is sit-bone width plus 20 mm, and we read down from there as you get lower |
| Moderate (MTB, gravel, hybrid) | +20 to +30 mm | SQlab suggests about +20 mm for a typical mountain-bike position; the upper half of the band is ours, for the more upright end of this group |
| Upright (city, trekking, cruiser) | +30 to +40 mm | Weight sits squarely on the bones, so both need support with margin; guides allow up to 4 cm |
One caveat the calculators skip: the cardboard measures you sitting upright, and the published studies show the contact points moving about a centimeter as posture changes. That is why the allowance shrinks as the position gets lower — the number you are adding to has already narrowed.
The same number, off the bike
Your sit-bone width sizes more than a saddle. The Socket Seat desk cushion has two openings 6″ apart, center to center, designed for widths of about 3.6 to 6.7 inches; the result above tells you whether yours lands inside that range, and the fit checker explains what borderline means. For why sitting at a desk hurts in the same two places as a bad saddle, read sit-bone width for bike saddles (and everything else). You can also print the openings at actual size and lay your cardboard on them.
Sources
Allowances: bike-components.de, Measure sit bone width & determine saddle width (up to 4 cm upright; none fully extended) · Singletracks, How to measure your sit bones (SQlab: about +20 mm for a typical MTB position, up to +40 mm) · BikeFit, Sit bones width measurement and saddle selection (the +20 mm example, and why upright measurements overstate a low position). SQlab, Saddle Width System states the principle without a public number table: the measurement “is then combined with the rider’s typical riding position, since a more aggressive posture shifts the pressure point further forward on the saddle.” Sit-bone width data: how far apart are sit bones. Measuring: how to measure your sit-bone width at home.