Units of Measurement
Understanding units is fundamental to sizing, comparing, and optimizing compressed air systems.
Why units matter
Compressed air is a compressible fluid. This means the same air occupies different volumes depending on pressure and temperature. That's why:
- 100 liters at 100 psig = ~14 liters at atmospheric pressure
- A "cfm" is not the same as an "scfm"
- Reference conditions matter
Main categories
- Pressure - PSI, bar, kPa, atmospheres
- Flow - CFM, SCFM, Nm³/h, FAD
- Power - HP, kW, specific consumption
- Temperature - Conversions and reference points
Quick conversions
| Need | Multiply by |
|---|---|
| bar → psi | × 14.5 |
| psi → bar | × 0.069 |
| HP → kW | × 0.746 |
| m³/min → cfm | × 35.3 |
Mental calculator
- 1 bar ≈ 15 psi
- 1 HP ≈ 0.75 kW
- 1 m³/min ≈ 35 cfm