Estimate bicycle crank length from leg, tibia, or inseam measurements, compare research and fit formulas, round to stock sizes, and check your current cranks.
Crank Length Formula
The calculator uses one of two formulas depending on the mode you select.
By Height (LeMond method):
By Inseam:
- Height — your standing height, converted to millimeters.
- Inseam — cycling inseam measured from floor to crotch in bare feet, converted to millimeters.
- Crank Length — distance from the bottom bracket spindle to the pedal axle, in millimeters.
The result is a starting point, not a hard rule. Cranks come in fixed sizes (most commonly 165, 170, 172.5, and 175 mm), so round to the nearest available length. Riding style, flexibility, and bike fit history can justify going shorter or longer than the formula suggests.
Reference Tables
Use these to sanity-check the calculator output against common sizing guidance.
| Inseam (cm) | Inseam (in) | Suggested Crank (mm) |
|---|---|---|
| Under 76 | Under 30 | 160 – 165 |
| 76 – 81 | 30 – 32 | 165 – 170 |
| 81 – 86 | 32 – 34 | 170 – 172.5 |
| 86 – 91 | 34 – 36 | 172.5 – 175 |
| Over 91 | Over 36 | 175 – 180 |
| Discipline | Typical Range | Notes |
|---|---|---|
| Road | 165 – 175 mm | 172.5 mm is the most common stock size. |
| Time Trial / Tri | 160 – 170 mm | Shorter cranks open the hip angle in aero position. |
| Mountain | 165 – 175 mm | Shorter cranks improve pedal-strike clearance. |
| Track | 165 – 170 mm | Shorter for cornering clearance and high cadence. |
Example and FAQ
Example: A rider with an 82 cm inseam: 820 mm × 0.216 = 177.1 mm. The nearest standard size is 177.5 mm, but 175 mm is more widely available and well within the acceptable range.
Does crank length really matter? Within a 5 mm window, most riders will not notice a power difference. Comfort, knee tracking, and hip angle are what changes most.
Should I go shorter than the formula suggests? Often yes. Many fitters now recommend cranks 2.5 to 5 mm shorter than traditional formulas, especially for riders with tight hips or aggressive aero positions.
Height or inseam — which is more accurate? Inseam. Two riders of the same height can have very different leg lengths, and the crank turns at the leg, not the torso.
Can I switch crank length without other changes? If you go shorter, raise your saddle by the same amount you shortened the crank. If you go longer, lower it. Reach to the bars also shifts slightly.
