Table of Contents
What Is SCFM?
SCFM (Standard Cubic Feet per Minute) is a measure of gas flow rate corrected to standard temperature and pressure conditions. Because gas volume changes with temperature and pressure (per the ideal gas law), simply measuring the actual volume flow does not tell you how much mass of gas is flowing. SCFM normalizes the measurement to standard conditions so that flow rates can be meaningfully compared.
ACFM (Actual Cubic Feet per Minute) is the measured volume flow at the actual operating conditions. Converting from ACFM to SCFM allows engineers to properly size compressors, piping, valves, and other pneumatic equipment regardless of the operating conditions.
SCFM Conversion Formula
Temperatures must be in absolute units (Rankine): T_R = T_F + 459.67. P_actual and P_std are absolute pressures (psia, not gauge).
Standard Conditions by Organization
| Standard | Temperature | Pressure |
|---|---|---|
| ASME / US Industrial | 68°F (20°C) | 14.696 psia |
| CAGI (Compressor) | 68°F (20°C) | 14.5 psia |
| ISO 2533 | 59°F (15°C) | 14.696 psia |
| API 2000 | 60°F (15.6°C) | 14.696 psia |
Applications
- Compressed air systems: Size compressors, dryers, and receivers using SCFM ratings.
- Process gas flow: Compare flow rates measured at different conditions.
- Pneumatic tools: Match tool SCFM requirements to compressor output.
- HVAC: Calculate ventilation rates standardized to reference conditions.
Frequently Asked Questions
What is the difference between SCFM and CFM?
CFM without qualification usually means ACFM -- the actual volume flow at operating conditions. SCFM is the equivalent flow at standard conditions. At higher pressures, a small ACFM can represent a large SCFM because the gas is compressed.
How do I convert SCFM to Nm3/h?
1 SCFM (at 68F, 14.696 psia) is approximately equal to 1.607 Nm3/h (at 0C, 101.325 kPa). The exact conversion depends on the standard conditions used for each unit.
Why does temperature matter for gas flow?
Gas expands when heated and contracts when cooled. The ideal gas law (PV=nRT) shows that at constant pressure, volume is proportional to temperature. A flow meter reading 100 ACFM at 200F contains less mass per minute than 100 ACFM at 68F.