Bike Gear Ratio
Calculator.
Enter your chainring, cog, wheel size, crank length and cadence to instantly get gear ratio, gear inches, gain ratio, metres of development and your speed.
Results update as you type. Gear inches and gain ratio are standard road-bike figures; adjust the wheel option to match your bike.
How the calculator works
Every figure comes from four numbers: your front chainring, your rear cog, your wheel size and your crank length.
Lower numbers mean easier gears for climbing; higher numbers mean harder gears that travel further per stroke but demand more force. Your real-world speed is always a trade-off between gear ratio and the cadence you can hold.
Bike gear ratio FAQ
For general road riding, a gear ratio between roughly 2.5 and 4.0 covers most situations. A 50T chainring with a 15T cog gives a ratio of 3.33, a versatile all-round gear. Climbers favour lower ratios (easier gears near 1.0), while flat-out sprinters use higher ratios above 4.0.
Divide the number of teeth on the front chainring by the number of teeth on the rear cog. A 50T chainring and a 25T cog is 50 ÷ 25 = 2.0. The higher the number, the harder the gear and the further the bike travels per pedal stroke.
Gear inches express how big a gear feels by referencing the old high-wheel (penny-farthing) bikes. The formula is gear ratio × wheel diameter in inches. It lets you compare gears across bikes with different wheel sizes on a single scale.
Gain ratio, developed by Sheldon Brown, factors in crank length as well as wheel size. It is the distance the bike travels for each unit the pedal travels, so it accounts for the leverage of your cranks. Because it is a pure ratio it works in any unit system, unlike gear inches.
Development (or "rollout") is how far the bike travels in metres for one full pedal revolution. It equals the wheel circumference multiplied by the gear ratio. It is the metric-friendly cousin of gear inches and is widely used in Europe and track cycling.
A bigger chainring (or smaller cog) raises the gear ratio, so you travel further per pedal stroke, but it also takes more force to turn. You are only faster if you can sustain the higher torque at a good cadence. Speed comes from the combination of gear ratio and the cadence you can hold.