CFM to SCFM Calculator: Convert Actual Flow to Standard Flow
Use this calculator to convert Cubic Feet per Minute (CFM) at actual conditions into Standard Cubic Feet per Minute (SCFM), based on your pressure, temperature, and ambient conditions.
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What Is the Difference Between CFM and SCFM?
CFM (Cubic Feet per Minute) and SCFM (Standard Cubic Feet per Minute) are both used to describe the volumetric flow rate of air, but they measure it under different conditions.
- CFM: Refers to the actual air volume flow rate at a given temperature and pressure.
- SCFM: Refers to the air volume flow rate corrected to standardized conditions (usually 14.7 PSIA and 68°F).
Why the Difference Matters
Compressible fluids like air change volume depending on pressure and temperature. So a system delivering 100 CFM at 90°F and 12 PSIA is not the same as 100 CFM at 68°F and 14.7 PSIA. This difference matters for:
- Comparing compressor ratings
- Sizing pneumatic tools
- Ensuring consistency across locations and climates
Conversion Formula
The general formula to convert CFM to SCFM is:
SCFM = CFM × (P_actual / P_standard) × (T_standard / T_actual)
Where:
Pis absolute pressure (PSIA)Tis absolute temperature (Rankine = °F + 459.67)
Full Example:
- CFM = 150
- Pressure = 13.7 PSIA
- Temperature = 90°F
- Standard pressure = 14.7 PSIA
- Standard temperature = 68°F
First convert °F to Rankine:
- T_actual = 90 + 459.67 = 549.67
- T_standard = 68 + 459.67 = 527.67
Then apply formula:
SCFM = 150 × (13.7 / 14.7) × (527.67 / 549.67) ≈ 132.5
SCFM Standard Conditions
Different industries may use slightly different standards. Common definitions:
| Standard | Temperature (°F) | Pressure (PSIA) |
|---|---|---|
| ANSI / ISA | 68°F | 14.7 |
| ISO 1217 | 68°F | 14.5 |
| Custom | User-defined | User-defined |
Applications
- Compressor Ratings: Manufacturers specify SCFM to allow apples-to-apples comparisons.
- Mass Flow Calculations: SCFM allows for more accurate modeling in combustion and mixing processes.
- Tool Matching: Air tools list SCFM to ensure compressors deliver enough usable air.
Tips for Accurate Use
- Always use absolute pressure (PSIA), not gauge (PSIG).
- If only PSIG is known, convert using: PSIA = PSIG + atmospheric pressure (14.7 at sea level).
- Temperature must be in Rankine (°F + 459.67).
FAQ
Q: Can SCFM be lower than CFM?
A: Yes — especially at low pressure or high temperature. At higher temp, air is less dense, so it expands and takes more volume (more CFM for same SCFM).
Q: Why use SCFM instead of CFM?
A: SCFM accounts for environment. CFM alone is meaningless without pressure/temperature.
Q: What if I only know PSIG?
A: Convert it to PSIA by adding atmospheric pressure. If you're at sea level, use 14.7 PSIA = 0 PSIG.
Conclusion
Using SCFM instead of raw CFM ensures consistency, safety, and compatibility across tools, compressors, and environments. This calculator simplifies the process of converting real-world airflow into standardized terms. Be sure to verify pressure and temperature inputs for best results, especially when working with high-precision pneumatic systems or performance-critical operations.