Spoke Length Calculator
Enter the rim and hub measurements to estimate the required spoke length for each wheel side.
A QUICK WALKTHROUGH
How to use this tool
- Measure the rim effective rim diameter (ERD) and hub flange pitch circle diameters.
- Enter the center-to-flange distances, total spoke count, and crosses.
- Calculate the left and right spoke length estimates separately.
Geometry and scope
This is a geometry-based estimate using the entered ERD, flange pitch circle diameter (PCD), center-to-flange distance, spoke count, and crosses. Left and right sides are evaluated independently. Length = sqrt(R² + r² + d² − 2Rr cos(θ)), where R = ERD/2, r = flange PCD/2, d = center-to-flange distance, and θ = 2π × crosses ÷ spokes per flange. This ideal hole-center geometry omits spoke-hole drilling correction and rim offset. Reference: https://www.parktool.com/assets/img/repairhelp/Spoke-Length-Worksheet.pdf; https://www.sheldonbrown.com/spoke-length.html
Measure carefully
Use millimetres for all dimensions. ERD is measured between the spoke seating points at the rim, not the outside rim diameter. PCD is measured through the centers of opposite flange holes.
Planning estimate
Confirm the result against the rim and hub manufacturers’ specifications and a wheelbuilding reference before ordering spokes. The tool does not account for every hub, rim, nipple, or lacing variation.
Local processing
All values are calculated in your browser and are not uploaded.
GOOD TO KNOW
Common questions
Why are two lengths shown?
The left and right flange distances or PCDs can differ, so each side is calculated from its own measurements.
What is ERD?
Effective rim diameter is the diameter measured at the points where the spoke nipples seat inside the rim.
Is this an exact spoke order specification?
No. It is a geometry-based estimate. Verify measurements and round to available spoke lengths using the component makers’ guidance.