 Calculating belt velocity and horsepower. Step one, calculating the circumference of the drive pulley. In this example, the pulley diameter is 6 inches and the pulley RPM is 1750. Step two, calculate the belt velocity by multiplying RPM by the circumference of the driver pulley. Step one, calculate torque in foot pounds. Torque equals radius times force. In this example, the radius equals 3. The radius equals the diameter of 6 inches divided by 2. So torque equals our radius of 3 times a force of 30 pounds. 3 times 30 equals 90 and we divide that by 12. So our torque equals 90 divided by 12 which equals 7.5 foot pounds. Step two, insert torque and RPM into the horsepower formula. You've completed calculating belt velocity and horsepower.