A belt drive having a 12 inch driver pulley and a 6 inch driven pulley has a pulley ratio of__________.

• A. 0.5
• B. 2.0
• C. 1.0
• D. 0.25

Answer: (A)

Pulley ratio is found by comparing the two pulley diameters in a belt drive. With the driven pulley at 6 inches and the driver at 12 inches, the ratio expressed as driven over driver is 6/12, which equals 0.5. This matches the given answer. It’s useful to connect this to how the belt moves: the belt carries the same length per revolution, so the smaller driven pulley must rotate more times to take up the same belt length. Specifically, for each turn of the driver, the driven makes two revolutions (12/6 = 2). If you instead defined the ratio as driver over driven, you’d get 2, which reflects the speed ratio, but the requested pulley ratio here uses driven over driver.