CalculatorsCrank Length Calculator
Crank Length Calculator
Crank length follows inseam in 4 cm bands. The second number is 2.5 mm shorter — the length many fitters try when hip angle or cadence feels cramped.
Inputs
Results
- Crank length
- 172.5 mm
- Shorter alternative
- 170.0 mm
How the number is made
Under 72 cm → 165 mm. From 72 up to 76 → 167.5. From 76 up to 80 → 170. From 80 up to 84 → 172.5. From 84 up to 88 → 175. At 88 cm and above → 177.5. The lower edge of each band is included. Shorter option = that length minus 2.5 mm, never below 160.
Shorter cranks lower the knee at the top of the stroke. Re-check saddle height after a change.
Related calculators
- Optimal Saddle Height Calculator
Change cranks and the LeMond mark needs another look.
- Bicycle Gear Ratio Calculator
Crank length is leverage; chainring teeth are the gear.
Questions
Is 172.5 the default for a reason?
It is the historical middle, not a measurement. An 82 cm inseam lands on 172.5. 80 cm starts that same band. 170 mm is only from 76 cm up to, but not including, 80 cm.
Will shorter cranks slow me down?
They change leverage and hip angle. Gear ratio and cadence decide speed, not the arm length alone.
Why is 80 cm not 170 mm?
The 172.5 mm band starts at 80 cm. 170 mm covers 76 cm up to, but not including, 80 cm.
Related gear
- Crank length options
Confirm BCD and spindle standard before you buy a shorter arm.
$80–$600