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
The Result is indicative and educational. It does not constitute a design, a technical opinion or medical advice and does not replace calculations or verification by a person with the appropriate qualifications and authorisations. Before purchase, installation or use in practice – in particular in electrical installations – the Result should be verified by a qualified specialist. Details: Terms of Service, point 4.
How the number is made
Under 64 cm → 160 mm. From 64 up to 68 → 162.5. From 68 up to 72 → 165. 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 and raise the pedal at the bottom, so raise the saddle by the length you took off and re-check saddle height. The bands are a starting rule of thumb, not a measurement of hip or knee range.
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.
What if my inseam is under 68 cm?
The bands keep stepping down 2.5 mm every 4 cm: 162.5 mm from 64 cm and 160 mm below that. 160 is also the floor for the shorter option, because few adult cranksets go shorter.
Example products
Product links are Affiliate Links to Amazon websites. Using them does not cost you anything extra, and if you make a purchase we may receive a commission. Details: Terms of Service, point 5.
- Crank length options
Confirm BCD and spindle standard before you buy a shorter arm.
$80–$600