Engineers measure the output of an industrial fan in terms of the number of cubic feet that it moves each minute (CFM). Some devices can measure this air flow along an enclosed path such an air duct. You can also, however, calculate this output from two other values associated with the fan's function. A fan that consumes more energy produces a higher output. A fan that creates a larger pressure differential also corresponds with a greater air flow.

Multiply the fan's energy consumption rate, measured in horsepower, by 530, a conversion constant. If, for instance, a fan works at 10 horsepower: 10 × 530 = 5,300.

Convert the pressure the fan creates, measured in pascals, to feet of water by dividing by 2,989. Each inch of water contains 249 pascals, and each foot of water contains 2,989 pascals. If the fan adds a pressure of, for instance, 1,000 pascals: 1,000 ÷ 2,989 = 0.335.

Divide the answer from Step 1 by the answer from Step 2: 5,300 ÷ 0.335 = 15,820. This is the fan's output in CFM.