Gear Ratio Calculator

Two riders on the same bike can be in totally different gears. The number that settles it is the gear ratio: chainring teeth divided by cog teeth. Pick your chainring, cog, wheel size and a cadence above, and the calculator returns the ratio, the gear in inches, how far one pedal stroke carries you, and your speed at that cadence.

What the four numbers mean

Gear ratio is the raw figure. A 50-tooth chainring on a 14-tooth cog gives 3.57, so the wheel turns 3.57 times for every full turn of the pedals.

Gear inches is the old-school way to compare gears across bikes with different wheels. It is the ratio multiplied by the wheel diameter in inches, which is what the wheel would measure if it were a direct-drive penny-farthing. Development is the same idea in metres: the distance you travel per pedal stroke. Higher numbers across all three mean a taller, harder gear that moves you further per turn but takes more force to push.

How to use the speed figure

The speed output ties cadence to your gear. Hold 90 rpm in a 50/14 on 700x25c tyres and you roll at about 40.6 km/h. Drop to a 50/17 at the same cadence and you slow down without changing how fast your legs spin.

That is the practical use. If you keep spinning out a gear on the flat, the calculator shows how much speed a taller gear buys you at the cadence you already hold. If you grind on every climb, it shows how much a smaller chainring or bigger cog drops the effort. To turn watts into the same speed, cross-check with the bike power and speed calculator.

Reading it for your terrain

Tall gears suit flat roads and descents. Low gears keep your cadence up when the road points uphill. Most riders want a spread wide enough to cover both without forcing the legs into a slow grind or a frantic spin.

Your power-to-weight number decides how tall a gear you can hold on a climb, so a strong climber spins a bigger gear up the same grade. Check yours with the power-to-weight calculator, then set your gearing to match the hills you ride.