SCFM to CFM Calculator
Convert standard cubic feet per minute to actual CFM, or back, for compressed air at your pressure, temperature and altitude, with the standard conditions shown.
0 for air at atmospheric pressure.
14.696 at sea level; lower at altitude.
Use the standard your equipment's rating was given at; compressor and tool makers don't all use the same one. The result updates as you type.
Actual flow
13.11 ACFM
100 SCFM ⇄ 13.11 ACFM at 114.7 psia and 80 °F (standard 14.7 psia, 68 °F)
| Actual absolute pressure | 114.696 psia = 100 psig + 14.696 psia |
| Pressure ratio (standard ÷ actual) | 0.1282 |
| Temperature ratio (actual ÷ standard, °R) | 1.0227 |
| ACFM per SCFM | 0.1311 |
What this page cannot tell you
Humidity. Moist air holds water vapour that takes up part of the volume; this dry-air calculation leaves it out, which can matter for blowers and process air on hot, humid days. It also doesn't cover gases other than air, or pressure drop through filters and hoses.
How to convert SCFM to CFM
- Choose the direction. SCFM to actual CFM, or actual to SCFM.
- Pick the standard. The reference conditions your rating uses, or enter your own.
- Enter the actual conditions. Gauge pressure, barometric pressure and temperature where the air is.
- Read the flow. With the pressure and temperature ratios shown.
10 situations where an SCFM to CFM converter helps
Matching a tool to a compressor
Tool ratings and compressor ratings may use different bases.
Sizing piping
Pipe velocity depends on actual volume at line pressure.
Blowers at altitude
Lower barometric pressure means more actual volume per SCFM.
Hot inlet air
Warm air takes more volume for the same mass.
Flow meter readings
Turn a meter's actual reading into standard flow.
Comparing spec sheets
Put two compressors on the same basis.
Pneumatic conveying
Actual velocity in a line from standard flow.
Aeration and process air
Blower selection starts from actual inlet flow.
Air receivers
Volume calculations at tank pressure.
Learning gas laws
A practical example of the combined gas law.
How the conversion works
SCFM is a flow measured at reference ('standard') pressure and temperature; ACFM is the volume the same air occupies at the actual conditions. By the combined gas law (OpenStax Chemistry 2e §9.2), P₁V₁/T₁ = P₂V₂/T₂ with absolute pressure and absolute temperature, so ACFM = SCFM × (P standard ÷ P actual) × (T actual ÷ T standard). Actual absolute pressure is the gauge reading plus barometric pressure; temperatures are converted to degrees Rankine (°F + 459.67).
There is no single standard. One preset is 14.7 psia and 68 °F, the CAGI/ASME basis given in the Roots 'SCFM vs ACFM' guidebook as reproduced by PD Blowers (which also specifies 36% relative humidity); another is 14.696 psia and 60 °F. Choose the one your rating uses, or enter custom values.
Limits: this is a dry-air, ideal-gas calculation. Humidity, which the full Roots formula includes, isn't corrected, and that can matter for blowers on hot, humid days. Other gases, filter and hose pressure drops, and compressibility at very high pressure aren't covered. Everything runs in your browser.
Sources
- OpenStax Chemistry 2e — 9.2 Relating Pressure, Volume, Amount, and Temperature — Combined gas law
- PD Blowers — SCFM vs ACFM with sample calculation (Roots guidebook) — Standard conditions 14.7 psia, 68 °F, 36% RH
Frequently asked questions
What is the difference between SCFM and CFM?
SCFM is flow at standard reference conditions; CFM (ACFM) is the actual volume at the real pressure and temperature.
How do I convert SCFM to ACFM?
ACFM = SCFM × (standard psia ÷ actual psia) × (actual °R ÷ standard °R). 100 SCFM at 100 psig and 68 °F is about 12.8 ACFM.
What are standard conditions?
They vary by standard — commonly 14.7 psia and 68 °F, or 14.696 psia and 60 °F. Use your rating's basis.
Why does altitude matter?
Barometric pressure falls with altitude, so the same standard flow occupies more actual volume.
Does humidity matter?
Yes, somewhat; this calculation is for dry air and doesn't correct for it.
Is gauge pressure the same as absolute?
No: absolute = gauge + barometric pressure (about 14.7 psi at sea level).
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