# Air Compressor Calculations & Efficiency Formula

Learn what you need to keep your air compressor equipment running efficiently with Lewis Systems easy-to-use air compressor calculations and formulas tool.

CFM Calculator

Pipe Velocity Calculator

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1. CFM of compressed air required to raise a known system pressure
to a desired system pressure:C2 = Required CFM total
C1 = Existing or known CFM
P2 = Desired pressure
P1 = Known Pressure EXAMPLE: A 75 HP Compressor rated at 320 CFM t 125 PSIG will hold only 85 PSI and we desire 125 PSI.C1 = 320 CFM
P2 = 125 + 14.7 (139.7)
P1 = 85 + 14.7 (99.7)
C2 = 448.39 Total CFM requiredWe need an additional 128.39 CFM to raise system pressure to the desired level.
2. Simple Energy Formula: Motor Efficiency = Cost per KW X .746 (Power Factor) X Hours of operation X Brake horsepower *Note: No electric motor is 100% efficient, most will average 92-95% efficient.
3. PSI VS. BHP (Rule of thumb): For every 1 PSIG pressure drop, BHP (Brake horsepower) goes down ½ %.