Crank Size Calculator
Enter your inseam and the type of riding you do. The calculator uses the 20.9% inseam rule, adjusts for riding style and picks the nearest standard crank length.
- Inseam based
- Road, MTB, gravel, TT
- Nearest standard size
A starting point only. A bike fitter can fine-tune crank length for injuries, flexibility and position.
Most bikes come with the same cranks, but riders do not. A bike might ship with 172.5 mm cranks whether you are 160 cm or 190 cm tall. Crank length sets how far your knee bends at the top of the stroke. Cranks that suit your leg length can ease hip and knee strain and help you pedal smoothly.
Crank length chart
Inseam to crank length for road bikes. Search for your inseam.
| Inseam (cm) | Height (approx cm) | Road (mm) | MTB (mm) | TT (mm) |
|---|---|---|---|---|
| 70 | 155 to 160 | 145 | 145 | 145 |
| 74 | 160 to 165 | 155 | 155 | 150 |
| 77 | 165 to 170 | 160 | 160 | 155 |
| 80 | 170 to 175 | 167.5 | 165 | 162.5 |
| 83 | 175 to 180 | 172.5 | 170 | 167.5 |
| 86 | 180 to 185 | 180 | 177.5 | 175 |
| 89 | 185 to 190 | 185 | 182.5 | 180 |
| 92 | 190 and up | 190 | 187.5 | 185 |
Mountain bikes often run a little shorter for pedal clearance over rocks. Time trial riders go shorter still to open the hip in a low position.
Inseam and crank length
Road, MTB and time trial. Slide your inseam.
The calculator rounds to the nearest common size between 155 and 180 mm. Shorter and longer cranks exist, but you may need to look for specialist makers.
How to find your crank length
Measure, multiply, round. Step through it.
Measure inseam
Barefoot, back to a wall, book pressed up firmly.
If you change crank length, adjust saddle height by the same amount. Going 5 mm shorter means raising the saddle about 5 mm.
Shorter or longer cranks
What changes when you change length. Pick a direction.
Less knee and hip bend at the top. Easier to spin fast and hold an aero tuck.
Matched to your leg using the inseam rule.
More leverage per stroke, but tighter hips and more knee bend.
Studies show power output hardly changes across a wide range of crank lengths. Comfort and position matter more than leverage.
Signs your cranks are too long
Common fit warnings. Tick any you notice.
Tick each item as you go.
If several of these apply, try cranks 5 mm shorter. Many riders feel the difference on the first ride.
What the result shows
Length and its effect. Each tile explains one result.
Nearest standard size.
The exact rule before rounding.
Adjusted for your bike type.
Diameter your foot travels.
How open your hip stays at the top.
Crank length is printed on the inside of the crank arm near the pedal, for example 172.5.
Frequently Asked Questions
No question matches that search.
What crank length should I use?
About 20.9% of your inseam. An 82 cm inseam suggests about 172.5 mm for road riding.
Are shorter cranks better?
For many riders, yes. They open the hip, ease knee strain and suit aero positions with little or no power loss.
What is the standard crank length?
170 mm on small frames, 172.5 mm on medium and 175 mm on large.
Does crank length affect saddle height?
Yes. Shorter cranks need a slightly higher saddle, by the same amount.
What crank length for a 5 ft 6 rider?
Usually about 165 mm, depending on inseam.
Should MTB cranks be shorter?
Often by 2.5 to 5 mm, for more clearance over rocks and roots.
Where is crank length marked?
On the inside of the crank arm near the pedal thread.
Pedal with cranks that fit you
Measure your inseam, apply the 20.9% rule and adjust for how you ride. If your knees or hips complain, a shorter crank is one of the simplest changes you can make.
More size calculators
Each one has its own calculator, worked examples and answers to common questions.