What is the difference between ACFM and SCFM?

ACFM is the volume of air actually flowing at the measurement point's pressure, temperature and humidity. SCFM restates that same mass of air at an agreed standard condition (commonly 14.7 psia, 68 °F, 36% RH), so two compressors can be compared fairly.

How many CFM does one compressor horsepower produce?

A rule of thumb is about 4 CFM per horsepower at 100 psig for a rotary screw and roughly 3.5 to 4 CFM per horsepower for a two-stage reciprocating unit. Use the nameplate or a flow meter for anything beyond a sanity check.

Does altitude change the conversion?

Yes. Lower barometric pressure at altitude means each actual cubic foot holds less mass, so SCFM falls even though ACFM is unchanged. Enter the local inlet pressure rather than sea-level pressure.

CFM Calculator & ACFM/SCFM Converter

All calculators

Formula

SCFM = ACFM × (Pa/Ps) × (Ts/Ta)

Unit system

Actual → Standard flow

Actual flow

cfm

Inlet pressure

psig

Inlet temp

°F

Relative humidity

Standard flow

93.3cfm

Standard: 14.7 psia, 68°F (20°C)

Power → flow estimate

Motor power

Type

Estimated flow

113cfm

Rule of thumb at 100 PSI.

How to use this calculator

Normalize measured actual air flow to standard conditions and estimate delivered CFM from compressor horsepower.

Pick imperial (CFM, psig, °F, HP) or metric (L/s, bar, °C, kW) units.
Enter measured flow, line pressure, inlet air temperature and relative humidity.
Read the SCFM result, which corrects the measured ACFM to standard conditions.
Enter motor horsepower and compressor type to cross-check the expected delivered flow.

Frequently asked questions

What is the difference between ACFM and SCFM?: ACFM is the volume of air actually flowing at the measurement point's pressure, temperature and humidity. SCFM restates that same mass of air at an agreed standard condition (commonly 14.7 psia, 68 °F, 36% RH), so two compressors can be compared fairly.
How many CFM does one compressor horsepower produce?: A rule of thumb is about 4 CFM per horsepower at 100 psig for a rotary screw and roughly 3.5 to 4 CFM per horsepower for a two-stage reciprocating unit. Use the nameplate or a flow meter for anything beyond a sanity check.
Does altitude change the conversion?: Yes. Lower barometric pressure at altitude means each actual cubic foot holds less mass, so SCFM falls even though ACFM is unchanged. Enter the local inlet pressure rather than sea-level pressure.