SCFM vs ACFM in Compressor Sizing: What Every Engineer Should Know

Why this matters

When you specify a 100 SCFM compressor, the actual airflow at your site might be 92 or 123 SCFM-equivalent, depending on the local temperature and barometric pressure. Get this wrong and your downstream equipment (dryers, filters, receivers) is undersized or oversized — both expensive mistakes.

The simple rule

Compressor specs are in SCFM. Site conditions are in ACFM. Convert before you compare.

How to convert

Use the ideal gas law:

$$ Q_{ACFM} = Q_{SCFM} \times \frac{T_{actual}}{T_{std}} \times \frac{P_{std}}{P_{actual}} $$

Where T is in absolute units (Rankine or Kelvin) and P is absolute (psia or bara).

Common pitfalls

1. Forgetting altitude: At 5000 ft elevation, barometric pressure is ~12.2 psia, not 14.7. A "100 SCFM" compressor delivers ~120 ACFM.
2. Hot summer intake: Air at 100°F is 5.8% less dense than at 68°F. Account for summer peak.
3. Mixing units in the same system: If your compressor is rated SCFM and your dryer is rated ACFM, size the dryer for ACFM and the compressor for SCFM, then convert.

Try it yourself

Use our SCFM to ACFM converter with your local conditions.