Spoke Length Calculator for Bike, MTB and E-Bike Wheels

Work out the exact spoke length for a bicycle wheel — road, gravel, MTB, BMX, track, fat bike or an e-bike hub motor. Pick the kind of wheel you are building, adjust the four measurements, and read the left and right lengths straight off. The diagram redraws as you type, so you can see what every number actually refers to.

1

Start from a wheel like yours

Optional — it just fills the boxes

2

The rim

mm
Effective rim diameter — the circle the spoke ends sit on.
A rough starting point only. Measure or look yours up.
Rim and hub must match.
Measure your ERD with two spokes

Take two spokes of a known length. Screw a nipple onto each until the spoke tip is exactly level with the slot in the top of the nipple. Drop both into holes on opposite sides of the rim and let them hang towards the middle, then measure the gap between the two spoke heads. If the heads overlap instead, enter that overlap as a negative number.

mm
mm

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3

The hub

Left is the non-drive / disc side

mm
mm
mm
mm
Flange Ø is the circle the spoke holes sit on, centre of one hole to centre of the one furthest away on the same flange — not the outside edge of the flange.
4

Lacing pattern

Left / right length under each

0× is radial, 3× is the everyday choice for 32 and 36 hole wheels. The dot shows how easily the spokes would meet the rim at that pattern.
5

Your spoke lengths

Left

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Right

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Tension balance
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Dish
—

How far the flanges sit off the rim’s centreline

Worst nipple angle
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80° or more laces easily, under 75° gets fiddly

These are typical figures, not your hub. Flange diameter and centre-to-flange vary by a few millimetres between models, and a few millimetres is the difference between a spoke that seats and one that does not. Measure your own hub with a caliper, or take the numbers off the maker’s spec sheet, before you order.

Where each number comes from

Schematic, not to scale. Hover or tab into a box above and the matching dimension lights up.

What that lacing looks like

Drawn to scale from your ERD and flange diameter.
Advanced: offset rims, straight-gauge details, hub motors
mm
Asymmetric rims only. Positive = spoke bed shifted towards the drive side.
mm
2.6 for most hubs, 2.5 for 14g-only, 3.0+ where a motor is drilled for 12g.
mm
Hub motors with holes grouped in twos: centre-to-centre inside one pair.

The four numbers a spoke calculator needs

Spoke length is not a property of the wheel size. A 29er and a 700c road wheel share a rim diameter and still take different spokes, because the hub underneath is a different shape. Four measurements decide it.

ERD — effective rim diameter

The diameter of the circle where the ends of the spokes finish once the nipples are seated. Not the bead seat diameter (622 mm for 700c), not the outside of the rim. Most 700c rims land between 592 and 610 mm. Get it from the rim maker, or measure it with the two-spoke helper above — a 2 mm error in ERD is 1 mm on every spoke.

Flange diameter

The diameter of the ring of spoke holes, centre of one hole to centre of the hole opposite. Sometimes called the PCD. Measuring the outside edge of the flange instead is the most common mistake there is, and it makes every spoke several millimetres too short. With calipers: measure across the outside of two opposite holes, then the inside, and average.

Centre to flange

How far each flange sits from the middle of the hub along the axle. Close to equal on a front hub; on a rear the drive side is pulled well in to clear the cassette, often to half the left figure. That is dish, and it is why a rear wheel needs two spoke lengths. If your spec sheet gives lock nut to flange instead, tick the box in the advanced panel.

Cross pattern

How many spokes each spoke crosses on the way out. 3-cross for 32 and 36 hole wheels, 2-cross for 24 and 28, radial only on a front wheel with no disc and no motor — a radial spoke transmits no torque at all.

MTB spoke length: 29er, 27.5 and 26 inch

Same calculator, different numbers. Three things catch people out.

Boost moved the flanges. A Boost 148 rear hub is 6 mm wider than a 142 and both flanges shift outwards, so a length that suited your old wheel will not suit the new one. Same for a 110 front against a 100.

A disc rotor dishes the front wheel too. A rim-brake front hub is symmetric and takes one length; a disc front hub does not, so check both sides.

Wide rims are often asymmetric. Plenty of modern MTB rims put the spoke bed 3–5 mm off centre. Enter that in the rim offset box or your two lengths will be wrong by several millimetres. For orientation only: 29er ERDs are usually 590–605 mm, 27.5 around 555–572, and 26in 528–548.

E-bike and hub motor wheels

A direct drive motor can have a flange diameter of 150–200 mm against the 40 mm of a normal hub, which changes most of the rules of thumb.

Use fewer crosses, not more. With a flange that large the spokes are already near tangential at 1-cross; going further drags them round until they meet the rim at an angle the nipple cannot follow. Most hub motors lace 1-cross, and a large motor in a 20 inch rim usually has to go radial. The dots under the cross buttons show exactly where that line falls for your build.

Paired spoke holes. Many large motors group their holes in twos rather than spacing them evenly, which gives a radially laced wheel a real angle to drive through. Measure the centre-to-centre distance within one pair and enter it; you will get the two slightly different lengths that flange needs.

Nearly every hub motor is drilled for 36 spokes, so buy a 36 hole rim. Straight 13g or 12g spokes are normal — if your motor is drilled to 3 mm or more, change the spoke hole diameter in the advanced panel.

DT Swiss, Mavic, Shimano and Hope hubs

There is no brand-specific formula. Every calculator, theirs included, runs the same geometry — what the branded tools add is a stored list of that brand's hub measurements. Find the three figures for your model and this calculator gives the same answer.

DT Swiss publish flange diameter and centre-to-flange in the technical data sheet for each hub. Hope and Shimano do the same — note that Boost and non-Boost versions of one hub are different wheels. Mavic factory wheels often use proprietary spokes with non-standard ends; for a broken spoke the original part number is the reliable answer, and this calculator is for a rebuild onto a standard J-bend hub.

Whoever made it, check the published figure against the hub in your hand. Geometry gets revised quietly between model years.

Which cross pattern for which wheel

The angle a spoke sweeps round the hub is 720 × crosses ÷ spoke holes degrees, which is why 3-cross behaves differently on a 24 hole wheel and a 36 hole one.

Pattern Angle on 32h Where it belongs
0× radial 0° Front wheels with no disc and no motor. Transmits no torque.
1× 22.5° Hub motors and other very large flanges.
2× 45° 24 and 28 hole wheels, and small flanges.
3× 67.5° The default. 32 and 36 hole road, gravel, MTB and BMX wheels.
4× 90° 36 and 40 hole tandem and cargo wheels with small flanges.

More crosses means a longer spoke and a more tangential pull — better for torque, harder on the rim if the nipple ends up crooked. The calculator flags that angle for you.

From the calculator to a box of spokes

  1. Measure the hub and rim yourself with a caliper, even if you found the numbers online.
  2. Note both lengths. A rear wheel needs half the spokes in each; a symmetric front wheel needs one length throughout.
  3. Round to the nearest available size — spokes come in 2 mm steps. Within 1 mm is ideal, 2 mm still builds, and if caught exactly between take the shorter: a spoke poking past the nipple slot will cut the rim tape.
  4. Order spares in each length, and check the nipple angle before committing. Under 75°, either drop a cross or plan on washers.

Spoke length FAQs

How accurate does a spoke length have to be?

Within 1 mm of the calculated figure is ideal and you will not notice the difference. 2 mm still builds a sound wheel, though a short spoke has less thread engagement and a long one may reach the nipple slot. Beyond that you are borrowing trouble.

Why are my left and right spokes different lengths?

The two flanges are not the same distance from the middle of the wheel. On a rear hub the drive side is pulled inwards to clear the cassette, so its spokes are shorter and steeper. A front disc hub does a milder version of the same thing.

What is ERD and how do I measure it?

The diameter of the circle where the spoke ends sit once the nipples are seated. Run a nipple down two spokes of known length until the tip is level with the nipple's slot, drop both into opposite rim holes and measure the gap between the spoke heads. ERD = twice the spoke length plus that gap.

Can I use one length for the whole wheel?

If the two figures are within about a millimetre, yes — the calculator says so when that happens. If they differ by 2 mm or more, order both; splitting the difference leaves one side short of thread and the other poking through.

Does this work for e-bike hub motors?

Yes. Enter the motor's flange diameter and centre-to-flange like any hub. Because motor flanges are so large, use 1-cross or radial, set the spoke hole diameter if the motor is drilled for 12 or 13g spokes, and fill in the paired hole spacing if the holes come in twos.

What about straight-pull hubs?

Same formula, but the effective flange diameter and offset are taken from where the spoke head seats rather than from a hole in a flange, and some designs angle the seat too. Use the manufacturer's own figures for a straight-pull hub.