← All tools

Bike Spoke Length Calculator

Work out the spoke length for each side of a wheel from the rim ERD, the hub flange dimensions, the spoke count and the cross pattern — and get the whole-millimetre length to order.

Rim
mm, 200 to 800 — where the spoke ends sit
even number, 8 to 48, both sides counted
mm, 0 to 30 — shifts the spoke bed right
Hub
mm, 20 to 120 — hole circle, not flange edge
mm, 0 to 80
mm, 20 to 120
mm, 0 to 80
mm, 0 to 6 — 2.6 is common
Lacing
0 for radial, up to a quarter of the spoke count

Spoke length is the hypotenuse from the hub's spoke hole to the rim's spoke hole. The in-plane distance comes from the cosine rule on the flange radius, the rim radius and the lacing angle — 720° divided by the holes per flange, times the number of crosses — and the flange's distance from the hub centre is then added with Pythagoras. The spoke hole radius is subtracted because the nipple swallows that much thread. A rim with an offset spoke bed sits towards the right flange, so the offset adds to the left side's lateral distance and subtracts from the right; if the rim is fitted the other way round, swap the left and right flange measurements. Spokes are sold in 1 mm steps, so the result is rounded to whole millimetres; when the two sides differ by 1 mm, use the longer length for both, at 2 mm use the average, and at 3 mm or more order two lengths. Measure your own rim and hub rather than trusting a manufacturer's list, and check the result against a known build before lacing: a millimetre of error only shows up once the wheel is nearly finished. This model assumes J-bend spokes, evenly spaced holes and a rim whose spoke bed radius is ERD ÷ 2; straight-pull hubs, offset drilling and hub motors need their own dimensions. Everything runs locally in your browser with no storage, uploads or network access.