How to Measure Bicycle Crank, Stem & Spoke Length

Replacing cranks, stems, or building wheels requires accurate measurements. Get it wrong and parts won’t fit—or the bike will feel off.

The short answer: Crank length = center of spindle to center of pedal hole. Stem length = center of steerer clamp to center of bar clamp. Spoke length uses ERD (Effective Rim Diameter), flange dimensions, and lacing pattern—use an online calculator. Common crank lengths: 165, 170, 172.5, 175 mm.

Here’s how to measure each component.

How to Measure Crank Length

Crank length is the distance from the center of the bottom bracket spindle to the center of the pedal hole (where the pedal attaches).

How to measure:

1. Remove the crank arm (or measure one still on the bike).
2. Place a ruler or caliper from the center of the spindle hole to the center of the pedal thread hole.
3. Read the length in millimeters.

Common crank lengths: 165, 167.5, 170, 172.5, 175 mm. Road bikes often use 170 or 172.5; mountain bikes 170 or 175. Shorter riders and those with knee issues may prefer shorter cranks (165–170); taller riders often use 172.5–175.

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How to Measure Stem Length

Stem length is the distance from the center of the steerer tube clamp to the center of the handlebar clamp, measured along the stem’s length.

How to measure:

1. Use a ruler or tape measure along the stem’s top or bottom.
2. Measure from the center of the steerer clamp bolt to the center of the bar clamp.
3. Common lengths: 60, 70, 80, 90, 100, 110, 120 mm.

Stem angle is the rise or drop from horizontal. A +6° stem angles up; a -6° stem angles down. Angle affects reach and bar height.

Handlebar diameter: Most modern MTBs use 31.8 mm; some older bikes use 25.4 mm. Road bars are typically 31.8 mm at the clamp. Measure the bar where the stem clamps.

How to Measure Spoke Length

Spoke length depends on:

• ERD (Effective Rim Diameter) — The diameter of the rim at the nipple seats, measured from the inside of the nipple holes. Often measured with nipples in place, then subtract 2× nipple length to get “true” ERD for calculators.
• Hub dimensions — Flange diameter, flange spacing (left/right from center), and center-to-flange distance.
• Lacing pattern — Cross pattern (e.g. 3-cross, 2-cross) affects spoke length.

Best approach: Use an online spoke length calculator (e.g. from DT Swiss, Sapim, or similar). Enter:

• Rim ERD (from manufacturer or your measurement)
• Hub dimensions (from manufacturer specs)
• Number of spokes and cross pattern

Manual calculation is possible but error-prone; calculators are more reliable.

Measuring ERD: Insert two spokes into opposite nipple holes, thread nipples partway, measure the distance between the inner ends of the spokes, then add the length of two nipples. Or use the manufacturer’s published ERD if available.

Crank, Stem & Spoke FAQs

Summary

• Crank: Center of spindle to center of pedal hole (165–175 mm typical).
• Stem: Center of steerer clamp to center of bar clamp (60–120 mm typical).
• Spoke: Use an online calculator with ERD, hub dimensions, and lacing pattern. Measure ERD from the rim’s nipple seats.