Spoke Length Calculator
Enter your rim ERD, hub flange figures, spoke count, and cross pattern to get the drive- and non-drive-side spoke lengths for your wheel build.
The number the whole wheel depends on
A hand-built wheel is only as good as its spoke length. Get it right and the wheel tensions evenly and holds true through a season of rocks and drops; get it wrong and no amount of truing will save a build where the nipples run out of thread. The maths is the standard wheelbuilding triangle — rim radius, flange radius, flange offset, and the lacing angle set by the cross pattern — solved for each side of the hub.
Building a wheel is also the moment to check your chain length and revisit tire pressure for the new rim width.
Frequently Asked Questions
What measurements do I need to calculate spoke length?
Five numbers: the rim's effective rim diameter (ERD), the hub's flange pitch-circle diameter (PCD, where the spoke holes sit) for each side, the offset of each flange from the wheel centre, the total spoke count, and the cross pattern. ERD comes from the rim maker or is measured with a gauge; the hub figures come from the hub manufacturer's spec sheet. The calculator does the geometry once you have them.
Why are the left and right spokes different lengths?
A rear wheel is 'dished' — the cassette takes up room on the drive side, so that flange sits closer to the centreline than the non-drive flange. That smaller offset changes the triangle the spoke forms, so the drive-side spokes come out shorter. Front wheels can be dished too, for disc-brake clearance. Because this tool computes each side from the offset you enter, it hands back both lengths rather than a single average.
What does the cross pattern change?
The cross number (0 for radial, or 2x, 3x, and so on) is how many other spokes each spoke crosses on its way from hub to rim. More crosses lay the spoke at a shallower, more tangential angle — better for transmitting the braking and drive torque a mountain bike puts through the wheel — and make it slightly longer. A 32-spoke wheel laced 3-cross is the classic, dependable MTB build; radial lacing is rare on the driven or braked side.
How precise does spoke length need to be?
Close matters. Aim within about a millimetre and round to the nearest length your spoke supplier stocks (commonly 2 mm steps). Too long and the spoke bottoms out in the nipple before it is tight; too short and there is not enough thread to reach proper tension. Always double-check the hub and rim figures against the manufacturer's published numbers before you order a whole set.
A calculation based on the figures you enter. Confirm your hub and rim measurements against the manufacturer's specs before ordering spokes — a wheel build is unforgiving of a wrong number.