Bicycle gear calculator
Enter the teeth on your chainring and rear sprocket, pick the tyre size and cadence, and see the gear ratio, gear inches, metres travelled per pedal turn and the speed that gear gives.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Enter the teeth on the front chainring and on the rear sprocket you are using.
- Choose the tyre size, or enter a measured circumference in millimetres.
- Enter your cadence in revolutions per minute (rpm) to see the speed.
- Gear ratio = chainring teeth ÷ sprocket teeth
- Development (m) = gear ratio × wheel circumference (m)
- Gear inches = gear ratio × wheel circumference ÷ π ÷ 25.4
- Speed (km/h) = development × cadence × 60 ÷ 1000; mph = km/h ÷ 1.609344
Worked example
50 × 17 with a 700×25C tyre (2.105 m): ratio 50 ÷ 17 = 2.94, development 2.94 × 2.105 = 6.19 m, gear inches 77.6. At 90 rpm the speed is 6.19 × 90 × 60 ÷ 1000 = 33.4 km/h (20.8 mph).
Tips
Compare setups by gear inches or development rather than by tooth counts: 39×26 and 34×22 differ in teeth but are close in feel. To find the cadence for a target speed, use the cycling speed calculator.
Frequently asked questions
What is a gear ratio?
It is the number of teeth on the chainring divided by the number on the rear sprocket. A 50-tooth chainring with a 17-tooth sprocket gives 2.94, so the rear wheel turns 2.94 times per pedal turn.
What are gear inches?
Gear inches are the gear ratio multiplied by the wheel diameter in inches, the size of the wheel of an old penny-farthing that would give the same gearing. Higher numbers mean a harder gear.
What is development?
Development, or roll-out, is the distance the bike travels for one full turn of the pedals: gear ratio times wheel circumference. It is given here in metres.
Are the tyre circumferences exact?
No. They are typical values from bike-computer charts for an inflated tyre under load. Pressure, rider weight and tyre brand change the real figure by about one percent. For exact results roll the bike one wheel turn on the floor, measure it and choose a custom circumference.