Compressed Air Consumption Calculator

Free-air demand of pneumatic cylinders, tools and leaks, the compressor size to choose with a margin, and the yearly energy cost, including what the leaks cost.

How it works

A compressor is rated by its free-air delivery (FAD): the volume of air at atmospheric pressure that it delivers. A cylinder uses a volume of air at the working pressure that depends on its size, and that volume corresponds to a larger free-air volume by the compression ratio.

Vfree = Vcyl × (pg + patm) ÷ patm, Vcyl = (Apush + Apull) × stroke

A leak through a small hole is choked (flow at the speed of sound) at normal working pressures: m = 0.0404 Cd A p0 ÷ √T0 in SI units for air, with Cd = 0.6. The result is the free-air flow of one leak; leaks run all the time, including when the machine is idle. The total with a margin gives the compressor size; a rule of thumb is 6.5 kW of compressor power per m³/min at 7 bar. Force and speed of the cylinders are in the Cylinder Force and Speed Calculator.

Worked example

Four cylinders of 50 mm bore, 20 mm rod and 200 mm stroke make 30 cycles per minute at 6 bar gauge; other consumers use 100 L/min of free air; there are three leaks of 1 mm diameter; margin 25 %; 4 000 hours a year at 0.12 per kWh.

  • Swept volume per cycle = (1 963.5 + 1 649.3) mm² × 200 mm = 0.723 liters; compression ratio = (6 + 1.01325) ÷ 1.01325 = 6.922; free air per cycle = 5.00 liters.
  • Cylinders: 5.00 × 30 × 4 = 600 L/min.
  • One 1 mm leak at 6 bar: 38.9 L/min; three leaks: 117 L/min (14 % of the total).
  • Total demand = 600 + 100 + 117 = 817 L/min; with 25 % margin the compressor must deliver 1 021 L/min (1.02 m³/min, 36 cfm).
  • Power ≈ 6.5 × 1.021 = 6.6 kW; energy cost ≈ 3 185 a year, of which the leaks cost 364.

Things to know

The compressor rating FAD is at the stated discharge pressure and inlet conditions. Altitude, high inlet temperature and wear reduce it: ask the maker for the FAD at your conditions.

Cylinders only use air when they move; the average consumption depends on the real cycle rate. For intermittent demand a receiver tank smooths the peaks and lets a smaller compressor serve.

Pressure drop in the pipework reduces the pressure at the cylinder, so the compressor must produce a higher pressure than the machines need. Every 1 bar of extra pressure raises the compressor power by about 7 percent.

Leaks are the biggest saving in most air systems. Check with an ultrasonic detector or soapy water, and shut off idle machines.

Air quality (dryers, filters) adds to the system energy but is needed for long-lasting valves and cylinders.

Common questions

What does FAD mean?

Free-air delivery: the volume flow of air from a compressor, expressed at atmospheric pressure and the inlet temperature. It is what you compare with the demand.

What does a 1 mm leak cost?

About 39 L/min at 6 bar, which needs about 0.25 kW of compressor power: roughly 1 000 kWh a year at 4 000 hours, or more if the compressor runs all the time.

How do I size the air receiver?

V = Q × t × patm ÷ Δp, where Q is the peak demand above the compressor delivery (free air), t the time of the peak and Δp the pressure drop allowed.

Sources

  • ISO 1217, Displacement compressors: acceptance tests; CAGI, Compressed Air and Gas Handbook (FAD, receiver sizing, leak flows).
  • US Department of Energy, Improving Compressed Air System Performance; Festo, Compressed air consumption technical notes.

Last reviewed: November 2, 2026