Spoke Length Calculator

Calculate precise spoke lengths for wheel building. Enter your hub dimensions, rim ERD, and lacing pattern.

Rim

ERD — Effective Rim Diameter (mm) Measure across the inside of the rim at the spoke nipple seats, or look up your rim's spec sheet.

Hub — Left flange

Left flange diameter (mm) Diameter of the circle through the center of the spoke holes on the left flange. Typically 45–60 mm. Left center-to-flange distance (mm) Distance from the hub axle center to the left flange face.

Hub — Right flange

Right flange diameter (mm) Right center-to-flange distance (mm) On rear wheels this is smaller (drive side) — typically 16–22 mm for cassette hubs.

Lacing

Spoke count

Cross pattern

Spoke hole diameter in flange (mm)

Formula & notes

Formula: L = √(R² + F² + O² − 2RF·cos θ) − SHD/2

R = ERD/2 · F = flange diameter/2 · O = center-to-flange distance · θ = cross × 2π ÷ (spoke count ÷ 2) · SHD = spoke hole diameter

ERD tip: Some rim manufacturers publish ERD. If not, thread two nipples fully, place them in opposite spoke holes, and measure the distance between nipple heads — this is your ERD.

Rear wheels: The drive side (right) flanges are closer to center due to the cassette, so right spokes are usually 1–3 mm shorter than left.