The form below attempts to cover all crank/rear hub/cassete combinations; all without resorting to JavaScript. 'Regular' cassettes are considered to be twelve cogs for fifty teeth and larger, ten cogs for those smaller. I've tried to select the most common tooth spreads for the cassetes that are covered. If your cassete has fewer cogs or different tooth counts, use the 'choose' form on the Calculator page. I've tried to cover measurements and results in both inches and in Metric. All input is accepted for all combinations. What does not fit is simply discarded. The default wheel size is 35X700C. If yours is different, you can find the circumference by putting a drop of fluid (example: water or oil) on the tread of your rear tire and rolling the bike forward through one revolution plus a bit on some smooth surface, like concrete. This should leave two spots on the ground. Measure the distance between their centers in whichever system is easier for you. Select the closest choice on the appropriate dropdown; most popular tire/wheel sizes are represented.