Gear Ratio is the ratio of the angular speed of the driving gear to that of the driven gear. Or to put it in other words it is the ratio of the number of teeth on the drive gear divided by the number of teeth on the driven gear. If you count up the number of teeth on the drive gear (X), and on the driven gear (Y), you set them in a ratio (X:Y). If the number can be reduced, you have to reduce it, for example a ratio of 60:15 should be put as 5:2.