Bike Gear Ratio Calculator
Find your bike's speed at any cadence by calculating the gear ratio from chainring and cassette teeth counts, wheel size, and pedaling rate. Essential for optimizing gearing before a climb or time trial.
About this calculator
A bike's speed is determined by how far it travels per pedal revolution and how fast you pedal. The gear ratio is first found by dividing chainring teeth by cassette cog teeth: gear ratio = chainring / cassette. That ratio is then multiplied by the wheel circumference (wheel diameter × π) to find the distance covered per revolution — known as development. Multiplying by cadence (rpm) gives distance per minute, and converting from inches or meters to miles per hour completes the picture. This calculator uses: speed (mph) = round((chainring / cassette) × wheelSize × π × cadence / 1609.34 × 100) / 100, where wheelSize is the wheel diameter in inches and 1609.34 converts meters to miles. Understanding this helps cyclists choose gears for target speeds on climbs or flat stages.
How to use
Suppose you have a 50-tooth chainring, an 11-tooth cassette cog, a 700c wheel (diameter ≈ 26.2 inches), and you pedal at 90 rpm. Apply the formula: speed = round((50 / 11) × 26.2 × π × 90 / 1609.34 × 100) / 100 = round(4.545 × 26.2 × 3.1416 × 90 / 1609.34 × 100) / 100 = round(33,601 / 1609.34 × 100) / 100 ≈ round(20.88 × 100) / 100 ≈ 20.88 mph. This tells you that in your 50×11 big gear at 90 rpm, you're traveling about 20.9 mph.
Frequently asked questions
What is a good gear ratio for climbing hills on a road bike?
For steep climbs, most cyclists benefit from a gear ratio below 1.5:1 — for example, a 34-tooth chainring paired with a 28- or 32-tooth cassette cog. This allows a comfortable cadence of 70–90 rpm without excessive muscular strain. Compact cranks (50/34) combined with an 11-32 cassette give a wide range that suits both climbs and flat roads.
How does cadence affect cycling speed for a given gear ratio?
Cadence and gear ratio multiply together to produce speed, so doubling your cadence doubles your speed in the same gear. At a fixed gear ratio of 4.5 (e.g., 50×11), going from 80 rpm to 100 rpm increases speed proportionally — roughly from 18.6 mph to 23.2 mph. Most road cyclists target 85–100 rpm for an efficient aerobic effort that minimizes joint stress.
What does gear development mean on a bicycle?
Gear development is the distance a bicycle travels forward with each complete pedal revolution, typically measured in meters. It equals the gear ratio multiplied by the wheel circumference. A development of 8–9 meters per revolution is typical for flat road riding at moderate speeds, while climbers often use 3–5 meters of development to keep cadence high on steep gradients.