Gas Flow Rate Calculator (SCFM Converter)
Convert Actual Flow (ACFM) to Standard Flow (SCFM) based on pressure and temperature.
Calculated Result:
How to Calculate the Flow Rate of Gas
Calculating gas flow is more complex than calculating liquid flow because gases are compressible. When the pressure or temperature of a gas changes, its volume changes significantly. This is why engineers distinguish between Actual Cubic Feet per Minute (ACFM) and Standard Cubic Feet per Minute (SCFM).
ACFM represents the volume of gas flowing through a specific point at the current operating pressure and temperature. SCFM represents that same mass of gas corrected to "standard" conditions, typically 14.7 PSIA and 60°F.
The Gas Flow Conversion Formula
The standard formula to convert actual flow to standard flow is derived from the Ideal Gas Law (PV=nRT):
SCFM = ACFM × (Pact / Pstd) × (Tstd / Tact)
Where:
- Pact: Actual Absolute Pressure (PSIG + 14.7)
- Pstd: Standard Absolute Pressure (usually 14.7 PSIA)
- Tact: Actual Absolute Temperature (°F + 459.67 for Rankine)
- Tstd: Standard Absolute Temperature (60°F + 459.67 = 519.67°R)
Example Calculation
Imagine you have a compressor delivering 100 ACFM at an operating pressure of 100 PSIG and a temperature of 100°F.
| Step | Calculation | Value |
|---|---|---|
| Convert Pressure to Absolute | 100 PSIG + 14.7 | 114.7 PSIA |
| Convert Temperature to Absolute | 100°F + 459.67 | 559.67°R |
| Apply Formula | 100 × (114.7 / 14.7) × (519.67 / 559.67) | 724.5 SCFM |
Why Flow Rate Accuracy Matters
Understanding gas flow is critical for sizing pipes, selecting control valves, and ensuring industrial processes operate safely. Because gas expands when heated or compressed, failing to account for temperature and pressure can lead to equipment failure or massive inefficiencies in pneumatic systems.