Spoke Length Calculator

In short A spoke is the third side of a triangle in three dimensions, and its length follows exactly from four measurements: the effective rim diameter, the hub flange diameter, how far that flange sits from the wheel centreline, and how many other spokes it crosses. The crossing number is what makes it non-obvious — a radial spoke runs straight out and is the shortest possible, and every crossing swings the rim end further round and lengthens it. With 32 spokes there are 16 per flange, so the holes are 22.5° apart, and a 3-cross spoke spans three of those: 67.5°. Two things about the result matter more than the arithmetic. First, almost every wheel needs TWO lengths, not one. A rear wheel is dished to make room for the cassette, so the two flanges sit at different distances from the centreline and the spokes differ, often by two or three millimetres; a disc front wheel is dished too. Second, the effective rim diameter must be measured rather than looked up. It is measured to where the nipple seats, and it varies between production runs of the same rim model. A published ERD is a starting point, and spoke length is unforgiving in both directions — too short leaves too few threads engaged, too long bottoms out or pushes through into the rim tape.