Gear ratio can be calculated by using the gears __ or __ of the driven gear divided by the driver gear.

• A. Diametral Pitch, Number of Teeth
• B. Pitch Diameter, Number of Teeth
• C. Pitch Diameters, Teeth Count
• D. Pitch Diameters, Number of Teeth

Answer: (D)

Gear ratio is determined by the relative size of the two gears, specifically how many teeth or what pitch diameter each gear has. When gears mesh with a fixed module or diametral pitch, the pitch diameter is proportional to the number of teeth, so both measures describe the gear’s size in a way that’s directly comparable between gears. Therefore, the ratio of the driven gear to the driver gear can be found by dividing the driven gear’s size by the driver gear’s size, using either the pitch diameters or the teeth counts. In practice, that means you can use the driven gear’s pitch diameter divided by the driver gear’s pitch diameter, or the driven gear’s number of teeth divided by the driver gear’s number of teeth. Diametral pitch alone isn’t a direct size measure for forming the ratio without converting to pitch diameter or teeth count, so it isn’t used on its own.