How to use the calculator
- Enter your inseam. Barefoot, back against a wall, with a hardcover book pressed up between your legs: measure from the floor to the spine of the book. If you don’t know it, enter your height and we estimate it (× 0.46), though measuring is better.
- Pick your discipline. For mountain and triathlon we take off 2.5 mm (we explain why below).
- Tell us your current crank length, if you know it. It is stamped on the inside of the crank arm, next to the pedal axle (“170”, “172.5”, “175”). With that, we show you what would change if you switched to the recommended length.
Save to My Bike stores your inseam, your height and your current cranks, and the saddle height and gear ratio calculators use them automatically.
How we calculate it
Classic chart. The one bike shops have used for years, in 2.5 mm steps:
| Inseam | Approx. rider height | Classic crank | Current trend |
|---|---|---|---|
| under 29.1 in (74 cm) | under 5 ft 3 in (161 cm) | 165 mm | 160 mm |
| 29.1-31.5 in (74-80 cm) | 5 ft 3 in to 5 ft 8 in (161-174 cm) | 170 mm | 165 mm |
| 31.5-33.9 in (80-86 cm) | 5 ft 8 in to 6 ft 2 in (174-187 cm) | 172.5 mm | 167.5 mm |
| 33.9-35.4 in (86-90 cm) | 6 ft 2 in to 6 ft 5 in (187-196 cm) | 175 mm | 170 mm |
| over 35.4 in (90 cm) | over 6 ft 5 in (196 cm) | 177.5 mm | 172.5 mm |
The height column uses an average inseam of 46% of height; your own proportions may differ, so go by inseam when you have it. Keep in mind that stock bikes come with cranks matched to the frame size, not to your legs, so yours may not be the length you need.
Current trend. We take 5 mm off the classic chart (never below 150 mm). It is the jump many pros have made in recent years: Pogačar went from 172.5 to 165 mm in 2024. Fitters like Phil Burt, who worked with British Cycling and Team Sky, estimate that 5 mm shorter cranks open the hip angle by 2-3%. And brands have followed: Canyon now offers 160 to 167.5 mm cranks on its road bikes, and SRAM makes them from 150 mm.
By discipline:
- Road, gravel and city: the current trend as is.
- Mountain: 2.5 mm shorter. A shorter crank clears the ground by more and strikes rocks and roots less, especially on full-suspension bikes with a low bottom bracket.
- Triathlon and time trial: 2.5 mm shorter. With your torso flat on the aerobars, your hip is very closed at the top of the stroke; a shorter crank opens it up.
Reasonable range: from 2.5 mm below the recommended length up to the classic one. Any crank in that range is fine. All three numbers for every inseam are in the crank length chart by inseam.
What the research says
- Peak power barely depends on crank length. Martin and Spirduso (2001) tested cranks from 120 to 220 mm with 16 trained cyclists. Between the best (145 mm, 1,194 W) and the worst (220 mm, 1,149 W) there was only a 4% difference. The 145 and 170 mm cranks produced more power than the 120 and 220 mm ones. Their conclusion: the optimal crank is about 20% of leg length, and the standard 170 mm does not hold back most adults.
- Each crank length has its own cadence. In the same study, optimal cadence dropped from 136 rpm with 120 mm cranks to 110 rpm with 220 mm. With short cranks, you spin faster for the same power.
- Your joints do the same work. Barratt and colleagues (2011) measured hip, knee and ankle power with cranks from 150 to 190 mm: at the right cadence, the split did not change.
- 5 mm doesn’t change efficiency. Ferrer-Roca and colleagues (2017) tested 12 cyclists on their usual cranks (172.5-175 mm), 5 mm longer and 5 mm shorter: efficiency was the same (20.1-20.4%). The longer one closed the hip and knee by 2-3°. Their advice: when in doubt, go shorter.
- On a mountain bike, faster response. In XC riders, 170 mm cranks reached peak power sooner than 175 mm cranks (Macdermid and Edwards, 2010).
- Big changes do show. Too and Landwer (2000) found that 35 mm jumps change hip and knee angles and sprint power.
What about long cranks? Zinn, which makes custom cranks from 130 to 220 mm, suggests 21-21.6% of your inseam, which gives longer numbers than the classic chart for long legs. It is the other school of thought: more leverage for low cadences.
What changes when you switch cranks
If you change cranks and keep everything else the same, here is what happens (example from 172.5 to 165 mm, 7.5 mm shorter):
| What | Change | Why |
|---|---|---|
| Saddle height | Raise 7.5 mm (0.3 in) | The pedal sits 7.5 mm higher at the bottom |
| Top dead center | Your foot ends up 15 mm lower relative to your hip | The saddle goes up and the pedal at the top comes down |
| Leverage | Every gear feels 4.5% harder | Torque is force × crank length |
| Foot speed | 4.3% slower at the same cadence | The pedal circle is smaller |
In practice:
- Cadence: you will raise it a little without noticing, or use a bigger cog. According to Phil Burt, the only real losses show up at very low cadences (below 30 rpm), like on very steep ramps in a big gear.
- Hip and knee: they open up at the top. That is the main reason to go shorter: less hip discomfort, less knee pressure, and an easier low position.
- Effective gearing: with less leverage, the same chainring and cog take a bit more effort. If that worries you, check your drivetrain in the gear ratio calculator.
- Clearance: on a mountain bike, shorter cranks give you more room over rocks and when pedaling through corners.
When switching is worth it
- Yes: if you are on the small side and your bike came with 170-172.5 mm cranks; if you have hip or knee discomfort at the top of the pedal stroke; if you ride very aero (triathlon, time trial); if you strike your pedals a lot on a mountain bike.
- Probably not: if you are comfortable, have no discomfort and the difference would be 2.5 mm. A new crankset costs money and the performance change will be minimal.
Common mistakes
- Changing cranks without touching the saddle. With cranks 5 mm shorter, your saddle ends up 5 mm too low.
- Choosing cranks by frame size instead of by your legs. Two riders on the same size can have inseams 2.4 in (6 cm) apart.
- Measuring your inseam without pressing up. It comes out short, and so does your crank length.
- Expecting more power. A longer crank does not give you “more leverage” for free: it changes the cadence where you perform best.
- Forgetting your power meter. If it is in the crank arm, you will have to replace it with the crank; if it is in the pedals, enter the new length in its settings.
To know where to set your saddle after the change, use the saddle height calculator, and if you are shopping for a bike, start with your size.
Frequently asked questions
What crank length do I need?
By the classic chart, 165 mm below a 29.1 in (74 cm) inseam, 170 mm from 29.1 to 31.5 in (74-80 cm), 172.5 mm from 31.5 to 33.9 in (80-86 cm) and 175 mm above that. Many riders now go 5 mm shorter to pedal with a more open hip.
Do shorter cranks reduce power?
Hardly at all. In the Martin and Spirduso study (2001), peak power varied by only 4% between 145 and 220 mm cranks, and it was higher with 145-170 mm than with 220 mm. With shorter cranks you pedal at a higher cadence to put out the same watts.
Why do pro cyclists use shorter cranks?
To open up the hip angle in very aero positions and spin faster. Pogačar went from 172.5 to 165 mm in 2024, and Vingegaard has tested cranks as short as 150 mm.
Do I need to change my saddle height with shorter cranks?
Yes: raise it by as much as you shorten the cranks. Going from 172.5 to 165 mm, raise the saddle 7.5 mm (0.3 in). At the top of the stroke, your knee and hip will close 15 mm less.
Is a 2.5 mm crank length change worth it?
For performance, almost never. A 2017 study (Ferrer-Roca and colleagues) found no change in efficiency with cranks 5 mm longer or shorter. If you have hip or knee discomfort, or ride very low, you may notice it.
Sources
- Martin JC, Spirduso WW (2001). Determinants of maximal cycling power: crank length, pedaling rate and pedal speed. Eur J Appl Physiol 84(5)
- Barratt PR et al. (2011). Effect of crank length on joint-specific power during maximal cycling. Med Sci Sports Exerc 43(9)
- Ferrer-Roca V et al. (2017). Acute effects of small changes in crank length on gross efficiency and pedalling technique during submaximal cycling. J Sports Sci 35(14)
- Macdermid PW, Edwards AM (2010). Influence of crank length on cycle ergometry performance of well-trained female cross-country mountain bike athletes. Eur J Appl Physiol 108(1)
- Too D, Landwer GE (2000). The effect of pedal crank arm length on joint angle and power production in upright cycle ergometry. J Sports Sci 18(3)
- Cyclingnews: why Jonas Vingegaard is using tiny 150 mm cranks (2025)
- Cycling Weekly: what the science says about shorter cranks (2026)
- Escape Collective: Canyon adds shorter crank options to its bikes (2025)
- Zinn Cycles: custom cranks