CalculatorsSpoke Length Calculator

Spoke Length Calculator

Enter the rim ERD and one hub flange. Left and right flanges often differ on a rear hub or a disc hub, so calculate each side.

Inputs

Rim ERD (in)Flange diameter (in)Flange offset (in)Distance from the hub centreline to the flange centre.Spoke countCross pattern

Results

Spoke length: 11.4 in

How the number is made

Length = √(R² + F² + O² − 2·R·F·cos θ) where R is ERD/2, F is flange diameter/2, O is the flange offset from the hub centre, and θ is 720° × crosses ÷ spoke count. ERD is nipple-seat to nipple-seat, so the hole diameter is not subtracted again.

One flange per calculation. A rear or disc hub needs a second run with the other flange diameter and offset. The length is measured to the centre of the flange spoke hole. ERD already ends at the nipple seat, so the rim hole is not subtracted. Half the flange-hole diameter is not subtracted either. Round to a length you can buy. A 1 mm miss is usually tolerable; 2 mm starts to hide the nipple or leave it proud.

Related calculators

Wheel Circumference Calculator
ERD is the rim; circumference adds the tyre for the GPS.
Cost per Gram Calculator
A lighter spoke is only a bargain if the price per gram saved is sane.

Questions

What is ERD?

Effective rim diameter: the diameter measured at the nipple seats, not the outer tyre.

Do I run the same length both sides?

Only if both flanges match. Disc and cassette bodies usually offset one flange.

Why is the rim hole not subtracted?

Length ends at the centre of the flange hole. ERD already ends at the nipple seat, so the rim hole is not subtracted again. The flange-hole radius is not subtracted either.

Related gear

Double-butted spokes
Order the calculated length per side. Rear drive-side is often shorter.
$1–$3 each

Disclaimer — no professional advice, no liability

These calculators are simplified estimates for education. They are not a bike fit, a structural inspection, or a torque specification that overrides the number printed on a part. Confirm chain length, spoke length, tire fit and bolt torque on the bicycle before you ride.

These calculators, pages and any related content are provided “as is” and “as available”, solely for general educational and informational purposes. They are simplified mathematical estimates, not a professional bike fit, a structural inspection, a manufacturer torque specification or a training, nutrition or medical plan.

Results can be wrong, incomplete or inapplicable to your frame, wheels, tires, drivetrain or suspension. You must independently verify every figure, assume all risk, and confirm chain length before you cut, spoke length before you lace, tire and rim compatibility before you inflate, and the torque printed on the part before you tighten it.

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