Estimate your bike saddle width from your sit-bone distance and riding posture, or find the sit-bone width a chosen saddle suits, in mm or inches.
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 general measurement-kit method: triathlon 0 mm, road race 10 mm, moderate road/gravel/MTB 20 mm, trekking 30 mm, and city 40 mm. These are posture examples, not a rule for every bicycle or saddle model. SQlab’s 621 models have a separate sizing guide. The result is a starting point, 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 |
| Road race / low posture | 10 mm | 130 mm | Low, extended road posture |
| Moderate road / gravel / MTB | 20 mm | 140 mm | Moderate sporty posture; a race posture may use +10 mm |
| Trekking | 30 mm | 150 mm | Comfort-oriented trekking posture |
| City / upright | 40 mm | 160 mm | Upright city posture |
Understanding Your Results
The primary value is the method’s saddle-width starting point, or the sit-bone distance obtained by reversing the formula. The reverse result is an algebraic interpretation, not a new body measurement. Supporting outputs show the posture addition and an illustrative ±5 mm comparison; the comparison is omitted if it would include nonpositive widths. Details show nearby 10 mm arithmetic grid marks, not available product sizes, a manufacturer tolerance or a measured uncertainty.
A product’s labeled maximum width may not equal its effective usable support width. In reverse mode, enter the effective support width specified by the manufacturer. Compare the result with the specific manufacturer and model fitting guide and, when possible, use a demo or return program. Changing an input unit converts the current quantity; result units can be selected independently.
Worked Example
A 120 mm sit-bone measurement in a moderate posture uses a 20 mm addition: 120 + 20 = 140 mm. The illustrative comparison is 135–145 mm. It is not a measured tolerance or a comfort guarantee.
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 and effective saddle width; Measure at Home Kit, posture additions and model exceptions, page 2.
