# Horsepower required to Compress Air

## Online horsepower calculator

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The horsepower required to compressed air can be calculated with the calculator below:

Theoretical horsepower required to compress one cubic foot of free air (atmospheric pressure) for single-staged, two-staged and three-staged compressors are indicated in the diagram below. In general - plus *15-20%* friction.

The power required to adiabatic compression of air can be expressed as

HP = [144 N P_{1}V k / 33000 (k - 1)] [(P_{2 }/ P_{1})^{(k - 1)/N k}- 1]

(1)

where

HP = horsepower

N = number of compression stages

k = 1.41 = adiabatic expansion coefficient

P_{1}= absolute initial atmospheric pressure (psi) (14.7 psi at sea level)

P_{2}= absolute final pressure after compression (psi)

V = volume of air at atmospheric pressure (cfm)

- adiabatic compression (or expansion) takes place without transmission of heat

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