Spoke Size Calculator
Enter the rim's effective rim diameter, the hub flange diameter and the distance from the hub centre to the flange. Add the spoke count and lacing pattern, and you get the spoke length to order for that side.
- ERD and hub based
- Radial to 4-cross
- One side at a time
Calculate the drive and non-drive sides separately. Most rear hubs, and front disc hubs, have different offsets on each side.
Spoke length comes from a triangle in three dimensions. One end of the spoke sits in the hub flange and the other in the rim nipple. The distance between them depends on the rim size, the flange size, how far the flange sits from the centre of the hub and how many other spokes each one crosses. Getting it right to the nearest millimetre lets the nipple thread fully without bottoming out.
Typical spoke lengths
Real builds as a sanity check. Search by wheel size or hub.
| Wheel | ERD (mm) | Flange (mm) | Offset (mm) | Spoke (mm) |
|---|---|---|---|---|
| 700c road front | 602 | 39 | 35 | 294 |
| 700c road rear, drive | 602 | 45 | 18 | 292 |
| 700c road rear, non-drive | 602 | 45 | 38 | 294 |
| 29er front disc, left | 600 | 58 | 32 | 291 |
| 27.5 MTB rear, drive | 560 | 57 | 22 | 270 |
| 26 in MTB front | 545 | 45 | 35 | 266 |
| 20 in BMX front, 36h | 391 | 45 | 33 | 187 |
| 16 in kids, 28h | 305 | 40 | 30 | 151 |
Your result should be close to a similar build here. If it is more than 5 mm away, recheck the ERD, which is the most common measuring mistake.
How the cross pattern changes length
Same rim and hub, different lacing. Step through the patterns.
More crosses send the spoke out closer to a tangent from the hub, which handles pedalling and braking torque better. That is why rear and disc wheels are usually laced 2 or 3-cross.
How to measure for spokes
Four measurements, all in millimetres. Step through the measuring.
Measure the rim ERD
Thread two spokes into nipples at opposite holes and measure end to end, then add twice the length past the nipple seat.
Rim and hub makers often list ERD, flange diameter and offsets in their technical data. Use published figures where you can, then check one by measuring.
Radial, 2-cross or 3-cross
The pattern changes strength and length. Compare the common lacing patterns.
Spokes run straight out from the hub. Light and stiff sideways but carries no torque.
Each spoke crosses two others. Common on 24 and 28 hole wheels.
The classic pattern for 32 and 36 hole wheels. Tough and easy to true.
Never lace a disc brake wheel or a rear drive side radially. The spokes cannot carry torque in that pattern and the hub flange can crack.
Before you order spokes
Double check the numbers. Tick each one.
Tick each item as you go.
Order a few spare spokes of each length. They are much easier to buy with the wheel set than to find later.
What the result tells you
Spoke length and the details behind it. Each tile explains one result.
To 0.1 mm, before rounding.
Rounded to the nearest whole millimetre.
Half the spoke count for each flange.
The angle each spoke turns through at the hub.
Your spoke count and cross pattern.
The calculator removes half of the 2.6 mm spoke hole diameter, because the spoke's bend sits in the middle of the flange, not at the edge.
Frequently Asked Questions
No question matches that search.
How do I calculate spoke length?
Use the rim ERD, hub flange diameter, flange offset, spoke count and cross pattern in the standard spoke formula. The calculator does the trigonometry.
What is ERD on a bike rim?
Effective rim diameter: the diameter at which the spoke ends sit inside the nipples. It is smaller than the rim's outer diameter.
Should I round spoke length up or down?
Round to the nearest millimetre. If you are exactly between two sizes, go down for thin rims and up for deep rims.
Why are drive and non-drive spokes different lengths?
The flanges sit at different distances from the hub centre to make room for the cassette or disc rotor.
What happens if spokes are too long?
The spoke pokes through the nipple and can puncture the tube, or the thread bottoms out before the wheel is tight.
What happens if spokes are too short?
Too few threads engage in the nipple and the nipple can pull off under load.
Is 3-cross always best?
It is the safe default for 32 and 36 hole wheels. Lower spoke counts often use 2-cross to keep the angle sensible.
Build wheels that stay true
Measure ERD and hub dimensions carefully, calculate each side separately and order to the nearest millimetre. Spokes of the right length tension evenly and keep a wheel true for thousands of miles.
More size calculators
Each one has its own calculator, worked examples and answers to common questions.