Turn a center-to-center sit-bone measurement and riding posture into a transparent saddle-width starting point, or reverse the method for a chosen saddle width.
How the Saddle Width Calculator Works
This calculator implements a sit-bone-plus-posture sizing method. It adds 0 to 40 mm to a center-to-center sit-bone measurement, depending on how upright the rider sits.
The posture additions follow SQlab’s transparent system: no addition for a very forward time-trial posture, then 10, 20, 30, or 40 mm as the rider becomes more upright. The result is a starting point with a ±5 mm trial band, not a universal width prescription.
Sit-Bone and Posture Formula
Formula or lookup: saddle-width starting point = sit-bone distance + posture addition
A more upright pelvis generally places the load on a wider portion of the sit bones. Forward rotation can narrow the supporting distance. The calculator therefore requires riding posture instead of adding the same amount for every rider.
Choosing the Right Inputs
Create two clear sit-bone impressions on corrugated cardboard or use a shop measurement system. Mark the center of each impression and measure center to center. Select the posture you actually sustain, not the posture you hope to hold briefly.
| Posture | Addition | Example with 120 mm sit bones | Typical starting use |
|---|---|---|---|
| Triathlon / TT | 0 mm | 120 mm | Very forward pelvic rotation |
| Stretched performance | 10 mm | 130 mm | Low, extended road posture |
| Moderate | 20 mm | 140 mm | Road, gravel, sport MTB |
| Slightly forward | 30 mm | 150 mm | Fitness and relaxed trail |
| Upright | 40 mm | 160 mm | City and trekking |
Understanding Your Results
The primary value is the method’s target width. Supporting outputs provide a practical trial range, the posture addition, and nearby 10 mm product sizes.
A product’s labeled maximum width may not equal its usable support width. Compare the calculator result with the same manufacturer’s own fitting system and, when possible, use a demo or return program.
Worked Example
A 120 mm sit-bone measurement in a moderate posture uses a 20 mm addition: 120 + 20 = 140 mm. The displayed trial band is 135–145 mm.
Common Mistakes
Do not measure the outside edges of impressions, use a soft couch that smears the marks, or assume more padding fixes a width mismatch. Do not select an upright addition for a posture that rotates the pelvis far forward.
Assumptions and Limitations
This method does not diagnose pain or account for pelvic asymmetry, saddle curvature, cutout shape, soft tissue, tilt, fore-aft position, leg-length difference, or movement on the bike. Persistent numbness, sores, or pain warrants a fit and health assessment.
Sources
SQlab GmbH. Sit Bone Measurement for Bike Saddles. Current fitting guide.
Specialized Bicycle Components. Bike Saddle Guide. Current online guide.