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.
New and Classic share this database
Both calculators on this page — the new one and the classic one — read that same database, so whichever you prefer, the rim and hub figures behind your answer are identical.
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, center-to-flange, axle width and spoke-hole diameter all come from the hub record, so you are not hunting specs across three tabs.
Classic is J-bend only — use New for straight-pull
The classic calculator is J-bend only, exactly as the original was. If you are building on a straight-pull or hooked-flange hub, use the new calculator — it is the one that knows the difference.
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.
What Classic covers, and what it leaves out
The classic calculator covers the core of that list: any cross count from radial to 4-cross, front and rear, J-bend hubs, and either picking a rim and hub from the database or typing your own measurements straight onto the diagram. It leaves out rim offset, straight-pull geometry and the laced-wheel preview.
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.
Entering your own ERD in either calculator
Measured your own ERD? Either calculator will take it. In the classic one you type it straight into the box on the rim diagram, and it overrides whatever the database holds for that rim.
Two calculators on one page
This page carries two spoke length calculators, and you can switch between them at any time with the New and Classic buttons above. Both read the same hand-verified rim and hub database, so the two can never disagree about a component.
The new calculator
The new calculator is the default. It searches rims and hubs by name, handles J-bend and straight-pull hubs, applies rim offset on asymmetric rims, previews the laced wheel and remembers builds you save.
The classic calculator
The classic calculator is the tool we ran for years, rebuilt. It is J-bend only; you pick a rim and hub from dropdowns or type measurements straight onto the diagram, and it ignores rim offset exactly as the original did. On a radial build that makes it read about a millimeter longer than the new calculator. It is here for anyone who learned on it and wants the answer it always gave.
Frequently asked questions
Can I still use the old spoke calculator?
Yes. Choose Classic at the top of this page. It is the calculator we ran for years — the same fields, the same diagram and the same arithmetic — now reading from our current rim and hub database.
Why do the two calculators sometimes differ by a millimeter?
Only on radial builds. The classic calculator applies the spoke-hole correction the way the original did and ignores rim offset, so a radial wheel reads about a millimeter longer. On crossed builds the two agree exactly.
How accurate is this spoke length calculator?
The math is exact for the numbers you give it. Accuracy comes down to the inputs — mainly ERD and hub center-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 millimeter.
What spoke length do I need if my rim is not listed?
Switch to manual entry and type your own ERD, hub flange diameters, center-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 center, 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 centerline 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 millimeter; 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.