Our bike gear calculator may help you in choosing chainrings and cogs. Many contemporary bicycles have multiple gears and thus many possible bike gear ratios. Select the range of interest and check which combination is best suited to your cycling preferences and conditions. As a result, you will get the tables in gear ratio and gear inches units.
Gears are used to increase the force or speed and gear ratio is a unit of bike gearing. To calculate the gear ratio, divide the number of teeth in front chainring by the number of teeth in a rear sprocket:
gear ratio = (number of teeth in front chainring) / (number of teeth in rear sprocket)
For example, if the number of teeth is even, the gear ratio equals 1. For 50 teeth in front and 25 in the back, the gear ratio is 2. For bicycles equipped with hub gears, the gear ratio also depends on the internal planetary gears within the hub, so gear ratio is not a good measure when planetary gears are involved.
Gear inches is another relative measure of bicycle gearing. It corresponds to the diameter of the main wheel of an old-fashioned penny-farthing bicycle with equivalent gearing. Gear inches is calculated as the gear ratio multiplied by wheel diameter (in inches) and is usually rounded to nearest whole number:
gear inches = wheel diameter * (number of teeth in front chainring) / (number of teeth in rear sprocket)
Why don't we use the chainwheel and rear sprocket teeth values as a measure of a gear? Let's answer with the question: do you know instantly that 39/14 is the same gear as a 53/19? Probably not. That way of showing the ratio is inconvenient and can be confusing. One value explaining taht the gear ratio (or gear inches) for both combinations equals 2.79 (or 78) is much easier.
Our bike gear calculator can show the ratios for the range of chainrings and cogs teeth so that you can check your bike gear ratios and gear inches in different settings: