Home/Tools/Spoke Length Calculator
Free wheelbuilding tool

Spoke Length
Calculator.

Enter your rim ERD, hub flange numbers, spoke count and cross pattern to get the left and right spoke lengths in millimetres.

Wheel numbers (mm)
Left (non-drive)
Right (drive)
Spoke length
Left
292.9 mm
Right
291.4 mm
Crossing angle 67.5°
Round to the nearest even millimetre. When you sit between two lengths, choose the shorter option for the drive side. Front wheels are usually symmetric, so both sides match.

Results update as you type. Accurate ERD and hub numbers are essential; check the maker's published figures before ordering spokes.

The maths

How the calculator works

Spoke length is a geometry problem. The tool solves the standard equation for each side of the wheel from five numbers.

ERD
Rim ERD The effective rim diameter to the nipple seat. The biggest single driver of spoke length.
FD
Flange diameter The circle the spoke holes sit on at the hub, also called PCD. Bigger flanges give shorter spokes.
W
Flange offset The distance from the hub centreline to each flange. It differs left to right on dished rear wheels.
x
Cross pattern More crosses wrap the spoke further round the hub and lengthen it. Three cross is the usual standard.
LR
Two sides Because rear wheels are dished, the tool solves the left and right sides separately for an accurate pair.

Wheel building rewards precision. Confirm your ERD and hub numbers against the manufacturer, double check the cross pattern you plan to lace, and order spokes to the nearest even millimetre for each side.

Want a printable wheelbuilding reference?
A one-page spoke tension and lacing cheat sheet is coming soon to our shop.
FAQ

Spoke length FAQ

Spoke length comes from wheel geometry: the effective rim diameter (ERD), the hub flange diameter, the flange offset from the hub centre, the spoke count and the number of crosses. This tool plugs those into the standard spoke length equation and gives a length for each side of the wheel.

ERD is the diameter the rim presents to the spokes, measured to the point the nipple seats. It is the single most important rim number for spoke length and is usually published by the rim maker. If you measure it yourself, use two spokes and a ruler across the rim to the nipple seats.

On a rear wheel the cassette pushes the drive-side flange closer to the wheel centreline, which increases dish and shortens the spokes on that side. The non-drive side sits further out, so its spokes are a little longer. That is why the calculator asks for each side separately.

Three cross is the standard for most 32 and 36 spoke wheels and gives a strong, comfortable build. Lower spoke counts often use two cross, and some front or aero builds use radial (zero cross). More crosses lengthen the spoke slightly, which is why the pattern is part of the calculation.

Reputable hub makers publish flange diameter (PCD) and the centre-to-flange distance for each side. If you cannot find them, measure the flange hole circle diameter and the distance from the hub centreline to each flange with calipers. Accurate hub numbers are essential.

Aim within about 1mm. A spoke slightly too long can bottom out in the nipple or poke through, while too short may not engage enough threads. When you are between two lengths, most builders round to the nearest even millimetre and choose the shorter option for the drive side.