Chainring and Cassette Calculator: Gear Ratios, Range and Speed

Every gear you have, your range, and what a different chainring would actually change.

Teeth, separated by commas. Up to three.
Every sprocket, smallest first.

The wheel and the rider

mm
Exact figure from the wheel size calculator.
mm
rpm

Gear range

—

Easiest gear
— km/h

At your cadence

Hardest gear
— km/h

At your cadence

Average step
—

T

Four ways to describe a gear

Gear ratio is chainring teeth divided by cog teeth. 34×34 is 1.0, meaning one crank turn is one wheel turn. Simple, and it ignores wheel size.

Gear inches is the ratio times the wheel diameter in inches — the diameter of the penny-farthing wheel that would give the same gear. Old-fashioned but still the common currency in the English-speaking world.

Development is how far you travel per crank revolution, in metres. The metric equivalent, and the most intuitive of the four.

Gain ratio is Sheldon Brown's, and it is the only one that accounts for crank length: wheel radius divided by crank length, times the ratio. It matters because a 165 mm crank and a 175 mm crank on identical sprockets are not identical gears — the shorter crank is a harder gear to push.

Range, steps and choosing a chainring

Range is your hardest gear divided by your easiest, as a percentage. A 10-52 Eagle cassette is 520%; a road 11-28 with a 50/34 is about 372%. More range means more hills and more top end, at the cost of bigger jumps between gears.

Steps are those jumps. Under about 15% you barely notice; over 18% you have to change cadence noticeably to bridge one. This is the real trade-off in gearing, and it is why a close-ratio road cassette still exists.

A chainring swap shifts the whole range, it does not widen it. Going from 32T to 30T on a 1× makes every gear about 6% easier — better on climbs, and you lose the same 6% at the top. If you are spinning out on descents and walking up climbs, the chainring is not the answer; the cassette is.

FAQs

What chainring size should I run on a 1x?

On a mountain bike with a 10-51 or 10-52 cassette, 30–32T suits most riders, 34T if you are strong or your trails are flat, 28–30T for steep terrain or a loaded bike. Put your cassette in above and try each one in the compare box — the speed column tells you more than any recommendation.

How do I work out speed from a gear?

Multiply the gear ratio by your wheel circumference to get metres per crank turn, then by cadence and 0.06 for km/h. At 80 rpm a 2.0 ratio on a 2280 mm wheel gives about 21.9 km/h.

Is a 1x really worse than a 2x?

It has bigger jumps for the same range, and fewer genuinely distinct gears than the sprocket count suggests. A 2× has more usable steps but a third of its combinations are duplicates, which the shaded cells above show. The 1× wins on simplicity and chain retention rather than on gearing.

Does crank length change my gearing?

Effectively yes, which is what gain ratio is for. A shorter crank gives you less leverage, so the same sprockets feel harder. Going from 175 to 165 mm is roughly equivalent to making every gear 6% harder.

Will a bigger cassette fit my derailleur?

Only up to its rated capacity, and a longer chain. Check the derailleur's maximum sprocket figure before buying, and re-run our chain length calculator — a bigger cassette almost always needs a longer chain.

The code behind this calculator

A simplified, open-source version of this tool is on GitHub — the gearing maths as readable, dependency-free code, with tests and a walk-through of how the sums work. Free to read, fork or build on. View the source on GitHub →