BMX Calculators

Three workshop tools in one spot. Work out spoke lengths for a wheel build, compare gearing in gear inches and rollout, or get your chain length right before you break a chain. Each calculator remembers your last numbers. If anything looks off, email us at help@luxbmx.com.

Workshop tools

Spoke Calculator

Enter your rim's ERD and your hub's measurements and we'll spit out some lengths for you! Email us at help@luxbmx.com if you get stuck.

1Rim

effective rim diameter — on the rim's spec sheet mm

2Hub

outer face of one locknut to the other — 100 mm front, 110 mm rear on most BMX mm
Flange diameter centre of a spoke hole to the one directly opposite
Flange position outer face of the locknut in to the middle of the flange hub centre line out to the middle of the flange

3Lacing

More options
mm
mm

Your spoke lengths

Left —mm
Right —mm

Fill in the rim and hub measurements and your lengths will appear here.

Got your lengths? Everything you need to lace it up.

Spokes Nipples Rims Hubs Spoke wrenches

A wrong measurement gives a wrong spoke, so check the manufacturer's specs and measure twice. If a length sits between two sizes, go with the shorter one.

Gear Calculator

Pick your chainring, cog and tyre for gear inches and rollout — or type in the gear you want and we'll find every combo that gets you there.

Gear inches
—
Rollout
—
inches per crank rev
Gear ratio
—
chainring ÷ cog
Tyre diameter
—
inches (outside)
Chainrings across, cogs down. Tap a cell to select it. Green cells are within ±1″ of your current gear.

Type the gear you want

Enter gear inches or rollout — they update each other.

Found your gear? Grab the parts to run it.
Race chainrings Rear cogs Sprockets Race tyres

Gear inches

The classic way to compare BMX gearing. Bigger number = harder to turn, faster top end. Most riders sit between 53″ and 57″; the old-school baseline is 44/16 on a 20″ wheel, which is 55″ on the nominal chart (roughly 54″ on a real tyre).
(chainring ÷ cog) × tyre diameter

Rollout

How far the bike travels for one full turn of the cranks. Same information as gear inches, just expressed as a distance. Handy if you think in metres.
(chainring ÷ cog) × tyre diameter × π

Why tyre size matters

A "20 inch" tyre isn't 20 inches. A 20×1.75 measures about 19.5–19.9″ outside, a 20×1 3/8 about 20.5″. That's up to a full gear inch of difference on the same chainring and cog, so charts that assume 20.0″ read a touch high. Use Custom and measure your own wheel for the most accurate number.

Accuracy

Tyre diameters here are typical measured values across common race tyres. Real-world numbers move with pressure, rim width and wear, so treat this as a very close guide rather than gospel.

Chain Length Calculator

Get the link count right before you break the chain. This can have errors, so if you are unsure at all shoot us an email at help@luxbmx.com or size up.

How to measure: centre of the bottom bracket to centre of the rear axle, with the wheel where you want it to sit (slammed is the usual start). The link count rounds up, so the axle ends up a touch further back than measured – pull the wheel back to tension.

–links
Exact length –

Chainstay is too short for those sprockets – check your numbers.

–Axle sits back
–Cut from 98-link
–Gear ratio

Need a new chain? Count the links, then pick your chain.

Chains Half-link chains Chain tensioners Chain breakers
LUXBMX Workshop ToolsAustralia's BMX experts