Gear ratio calculator

How the calculator works

The gear ratio is the teeth on your chainring divided by the teeth on your sprocket. A 34 tooth chainring with a 34 tooth sprocket gives a ratio of 1. Your back wheel then turns once for each turn of the pedals.

Gear inches is an old way to compare gears. It is the size of your wheel in inches times the gear ratio. Sheldon Brown says the lowest gear on most mountain bikes is about 22 to 26 gear inches. The top gear on a road racing bike is often about 108 to 110.

Metres for each pedal turn is how far the bike rolls when your pedals go round once. Some riders call this development. Your speed is that distance times your cadence.

Gears for climbing

A bigger sprocket at the back gives you a lower gear. Each pedal turn feels lighter, but you go less far. On a hill that trade is often worth it. The table shows every gear on your back wheel, so you can see how low your easiest one goes.

Where the numbers come from

• The sums for gear inches and metres per turn come from Sheldon Brown's guide to gear sizes.
• Most wheel sizes come from the wheel size table in the Garmin Edge 830 manual.
• Garmin does not list 650b x 47 or 27.5 x 2.2. For those we added the rim size to twice the tyre width, then multiplied by pi. That method is on Sheldon Brown's bike computer page.
• The 11 to 34 set of sprockets is the Shimano HG800 11 speed cassette.

Tyres from different brands are not all the same size. Sheldon Brown says tables like this one are usually right to within 1 or 2 per cent.