Orifice Flow to SCFM Calculator
This formula estimates the flow of compressed air through a sharp-edged orifice (or leak) based on the orifice diameter and pressure differential. It is an empirical approximation...
Formula
Source: Engineering Toolbox, Compressed Air Challenge | Last reviewed: June 8, 2026
Examples
0 SCFM
= 90.6 SCFM
- orifice_dia = 0.25
- P_up = 100
- P_down = 0
1/4" hole at 100 psig leaks ~91 SCFM
0 SCFM
= 22.7 SCFM
- orifice_dia = 0.125
- P_up = 100
- P_down = 0
1/8" hole = 22.7 SCFM leak
0 SCFM
= 256 SCFM
- orifice_dia = 0.5
- P_up = 100
- P_down = 50
1/2" orifice with 50 psig back-pressure
Where is this used?
Relief valve and safety valve flow capacity estimation.
Flow metering orifice sizing for differential pressure flow measurement.
Pneumatic system troubleshooting and energy audit calculations.
Frequently Asked Questions
What is the typical cost of a compressed air leak?
A 1/4" leak at 100 psig (~91 SCFM) costs approximately $11,800/year in electricity at $0.10/kWh. Even a tiny 1/16" leak (~5.7 SCFM) costs ~$740/year. This is why leak detection and repair programs have rapid payback.
Does the orifice shape matter?
Yes. Sharp-edged orifices have a discharge coefficient Cd ≈ 0.62, which is built into this formula. Rounded or bell-mouth inlets flow more (Cd up to 0.98). Irregular holes from corrosion may flow differently. This assumes a clean sharp-edged orifice.
What about choked flow conditions?
When the pressure ratio P_down/P_up is below the critical ratio (~0.53 for air), flow becomes choked (sonic velocity at the orifice). This formula approximates both subsonic and choked flow regimes for compressed air service.
Reviewed for accuracy
· Last reviewed: June 8, 2026
All calculations are for reference only. Always verify with manufacturer data and a qualified engineer for critical applications. Learn about our editorial process.