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Spoke Length Calculator — Precise Spoke Lengths for Wheel Building
Calculate exact spoke lengths from hub and rim dimensions for wheel building.
How We Calculate This
Spoke Length Formula
- R = ERD / 2 (effective rim radius)
- r = Hub flange PCD / 2 (flange radius)
- d = Flange offset from hub centre
- theta = 720 × crosses / total spoke count [= 4 × pi × crosses / total spokes in radians]
- L = sqrt(R² + r² + d² − 2Rr cos(theta)) − spoke hole radius
- Result rounded to nearest 0.5 mm for standard spoke ordering
Frequently Asked Questions
ERD is the diameter of the circle where the spoke nipple ends sit in the rim. It is measured from the top of one nipple seat to the opposite side. Most rims have ERD stamped or available from the manufacturer.
Measure the diameter of the circle through the centre of the spoke holes on the flange (PCD - Pitch Circle Diameter). This is usually 38-65 mm for road hubs.
3-cross is standard for most wheels. 2-cross works for low-spoke-count wheels (24 spokes). Radial (0-cross) is used for front non-disc wheels only. Higher cross = stronger but heavier.
Within 1mm is ideal. Too short and you cannot get enough nipple engagement. Too long and the spoke may protrude through the nipple. Order to the nearest 1mm or 2mm available.
Rear hub flanges are asymmetric — the drive side is closer to centre. This means different spoke lengths for each side. The calculator gives one side; repeat with different flange offset for the other side.
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Last updated: March 2026
All calculations are estimates. Always verify results and consult a professional bike fitter where appropriate.