I need to check my crank length. How can I accurately measure it? Do I just use measuring tape as I was nervous of this because of the small difference between sizes I.e 172.5 175

  • 4
    Sometimes it is written on the back side of the crank.
    – rvil76
    Commented Jul 29, 2022 at 11:13
  • Thanks, I will check that
    – Charlie
    Commented Jul 29, 2022 at 11:34
  • If your bike is worth less than $1000USD or so, you can be pretty sure it's either 170 or 175. 172.5 and the other more exotic lengths aren't regularly found below that price point in my experience.
    – MaplePanda
    Commented Jul 30, 2022 at 6:48

2 Answers 2


Crank length is measured from the centre of the bottom bracket axle to the centre of the pedal axle.

It's explained here

Measuring tape should do, crank length goes in steps of 0.25cm (one tenth of an inch).

  • 2
    Steps in 2.5 mm* (one tenth of an inch)
    – Paul H
    Commented Jul 29, 2022 at 16:41
  • You're totally right. I'm getting old. But still, it's not hard to measure with a tape measure or a ruler.
    – Christine
    Commented Jul 29, 2022 at 18:34
  • When measuring, check the measurement a couple of times to be sure, to verify that you did not move your starting point/frame of reference.
    – Ted Hohl
    Commented Jul 29, 2022 at 20:24
  • 2
    Another trick is measure the largest distance between the hole edges, then smallest distance, add together and divide by 2. Removes need to find the center of both holes.
    – mattnz
    Commented Jul 29, 2022 at 20:59
  • But I'm with rvil76, I checked my Ultegra cranks, it mentions 175 on the back, I checked a 105 crank, also has it stamped in the back of the crank.
    – Christine
    Commented Jul 30, 2022 at 14:49

Measure it by looking around for where the length is written or stamped into it. Usually on the inboard side near the threads for the petal.

No tape measure required.

  • True, but is it possible that some low cost bikes may not have the length stamped on the crank?
    – Weiwen Ng
    Commented Jul 30, 2022 at 22:14

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