Free spoke length calculator for bicycle wheel building
Work out the exact spoke length for any wheel build — road, gravel, mountain, track, BMX, tandem, fat bike or e-bike. Pick your rim and hub from our database and the calculator returns the left and right spoke lengths for that wheel, or enter your own measurements if you are building with something we do not list. It is free, there is no sign-up, and nothing you enter is stored on our servers.
Built on a hand-verified rim and hub database
The calculator ships with 3,900+ rims and 5,100+ hubs from 380+ brands, including DT Swiss, Shimano, Hope, Chris King, Industry Nine, White Industries, Reserve, Boyd, Velocity, Nox Composites, H Plus Son, Kinlin, Ibis, Phil Wood, Onyx, Enve, WTB, Astral, Stan’s NoTubes, Race Face, Spank, Sun Ringlé and Velo Orange. Rim ERD, inner and outer width, section depth and asymmetric offset are checked against each manufacturer’s own published specification rather than copied from a spreadsheet — including 157 asymmetric (offset) rims, where ignoring the offset throws the dish out on every spoke.
J-bend, straight-pull and hooked-flange hubs
Straight-pull hubs use a different geometry from J-bend, and using the J-bend formula on one gives the wrong answer. This calculator switches formula automatically for the 179 straight-pull hubs in the database and for hooked-flange hubs such as the Onyx hook-flange range. Flange diameter, centre-to-flange, axle width and spoke-hole diameter all come from the hub record, so you are not hunting specs across three tabs.
What the calculator handles
- Every lacing pattern — radial (0-cross), 1-cross, 2-cross, 3-cross and 4-cross, with a recommendation for your hole count and flange diameter.
- Split left/right lacing — a different cross count per side.
- 2:1 (twin) lacing for 21, 24 and 27 hole builds.
- Asymmetric and offset rims, with the offset applied in the direction that actually reduces dish.
- Front and rear wheels together — build a whole wheelset, and shared choices carry across so you set them once.
- Nipple type and spoke washers — internal or external nipples, and washer allowance where the rim is measured with them fitted.
- Effective Rim Diameter (ERD) shown and editable, so you can override it with your own measurement at any time.
How to measure ERD
ERD is the single most important number in the calculation — a 1 mm error in ERD moves the spoke length by about 0.5 mm. The traditional definition is the diameter across the points the spoke ends reach, with the spoke entering the nipple by roughly 1.5 mm. Measure it with two old spokes and nipples fitted opposite each other, or use the value we hold for your rim and check it before you cut.
Frequently asked questions
How accurate is this spoke length calculator?
The maths is exact for the numbers you give it. Accuracy comes down to the inputs — mainly ERD and hub centre-to-flange. Our figures come from manufacturer specifications, but rims and hubs vary between production runs, so treat the result as a strong estimate and confirm before ordering. Round to the nearest whole millimetre.
What spoke length do I need if my rim is not listed?
Switch to manual entry and type your own ERD, hub flange diameters, centre-to-flange measurements and axle width. The calculator works entirely from those numbers, so a rim or hub we do not stock is no obstacle.
Do straight-pull hubs need a different calculation?
Yes. Straight-pull spokes leave the flange at a fixed angle set by the hub, so the J-bend formula does not apply. This calculator detects a straight-pull hub and switches to the correct geometry automatically.
Why are my left and right spoke lengths different?
On a dished wheel — any rear wheel with a cassette, and any disc-brake front — the flanges sit at different distances from the centre, so each side needs its own length. The calculator always shows both.
What is rim offset and does it change spoke length?
An asymmetric (offset) rim has its spoke bed moved sideways from the centreline to even out spoke tension. It changes both lengths, so it must be included. We hold the offset for every asymmetric rim in the database.
Should I round spoke length up or down?
Spokes come in 1 mm increments. Round to the nearest millimetre; if you land exactly between two sizes, the shorter spoke is usually the safer choice on a rim with standard nipples.
Once you know your lengths, order spokes, browse rims and hubs, or let us build the wheel for you with the Custom Wheel Program.