Compressed Air Flow to HP Calculator
A widely used industrial rule of thumb is that 1 horsepower produces approximately 4 SCFM of compressed air at 100 psig. This is a first-order approximation that accounts for...
Formula
Source: Engineering Toolbox, Compressed Air and Gas Institute (CAGI) | Last reviewed: June 8, 2026
Examples
100 SCFM
= 25 hp
100 SCFM requires ~25 HP compressor
400 SCFM
= 100 hp
400 SCFM = 100 HP typical
20 SCFM
= 5 hp
20 SCFM = ~5 HP (small workshop compressor)
Where is this used?
Energy auditing: estimating the electrical power draw from a known air flow.
Budgeting: rough capital and operating cost estimates for compressed air systems.
Frequently Asked Questions
How accurate is the 4 SCFM/HP rule?
It is a rough estimate, typically ±20%. Single-stage reciprocating compressors may deliver 3-3.5 SCFM/HP. Two-stage compressors deliver 4-5 SCFM/HP. Rotary screw compressors vary by pressure and size. Always verify with manufacturer data for final sizing.
Does pressure affect the HP requirement?
Yes, significantly. The 4 SCFM/HP rule assumes ~100 psig discharge. At 175 psig, the same compressor delivers only 3-3.5 SCFM/HP. At 50 psig, it may deliver 5+ SCFM/HP. Use the manufacturer's performance curve for accurate sizing at your pressure.
What about multi-stage compressors?
Multi-stage compressors with intercooling are more efficient, delivering closer to 4.5-5 SCFM/HP at 100 psig. The intercooling reduces the work of compression in subsequent stages, improving overall efficiency.
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.