Gear math for riders who think in mph.

Punch in your chainrings, cassette and wheel, and see exactly what every gear gives you — gear ratio, gear inches, gain ratio, development, and speed at any cadence. Imperial by default, because that’s how US riders search. One tap on the units switch flips the whole page to metric for everyone else.

Units
Speeds in mph · gears in gear inches
Your drivetrain

Set up your bike

Start from a common factory build, or dial in your own rings and cogs. Everything below updates instantly.

Start from a preset
Front chainrings

Teeth per ring, biggest first. Up to three rings.

Rear cassette

Edit the list directly to model any cassette — separate teeth counts with commas or spaces.

Wheel
Tire
Cranks

Crank length only affects gain ratio.

Gear chart

Every gear, one grid

Each cell is one gear combination. Tap any cell to inspect it.

Selected gear Overlaps another combo within 2% — a near-duplicate gear
Selected gear
—
Speed at cadence
— mph
Gear ratio
—
Gain ratio
—
Gear inches
— in
Development
— m / rev
90 rpm
Speed curves

Speed at cadence, by cog

One line per cog on the selected chainring. The bold line is your selected gear; the dashed line is your cadence.

Head to head

Compare against another setup

Same wheel, tire and cranks — only the gearing changes. Handy when you’re deciding between a road double and a 1× gravel build.

The math

How the numbers work

Four measures, each answering a different question. Gear inches is the US tradition; development is its metric twin.

Gear ratio

ratio = chainring teeth ÷ cog teeth

How many times the rear wheel turns for one full turn of the cranks, before wheel size enters the picture. A 52×11 is 4.73 — the wheel spins 4.73 times per pedal revolution.

Gear inches

gear inches = ratio × wheel diameter (in)

Named for the penny-farthing era: the diameter of the giant front wheel a gear is equivalent to. Higher is harder and faster. Wheel diameter includes the tire, so a wider tire raises every gear slightly.

Development

development = ratio × wheel circumference

How far the bike travels per pedal revolution, in meters — the metric counterpart to gear inches. If you know your cadence, this is the direct route to speed.

Gain ratio & speed

gain = ratio × (wheel radius ÷ crank length)

Sheldon Brown’s refinement: it folds in crank length, so it compares effort fairly across bikes. Speed then follows from cadence: speed = cadence × development × 60.