Air Compressor Running Cost Calculator: Specific Power and Cost of Leaks

Turn the kW on a screw compressor controller into a yearly running cost, a cost per cubic metre of air, and what leaks are costing you.

Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.

How this calculator works

Specific power is the electrical power divided by the air delivered. For a fixed-speed oil-injected screw compressor at about 7 bar it is usually roughly 6 to 7.5 kW for each m³/min of free air. A much higher figure points to a worn, dirty or oversized machine, or a free air delivery figure that is for a different pressure.

The compressor draws full power while loaded and a smaller share while unloaded, so the average power depends on the share of time it spends loaded. Multiplying the average power by the hours and the electricity price gives the yearly cost. Leaks are costed as their share of the air produced while loaded.

Formulas used

  • SP = \frac{P}{FAD \times 0.06}
  • P_{avg} = P\,[\,L + (1 - L)\,I\,]
  • C = P_{avg} \times h \times \text{price}

Worked example

With the default numbers in the calculator above:

  1. Specific power (kW for each m³/min of free air): 6.06 kW per m³/min (0.36 kW per L/s)
  2. Energy for each cubic metre of free air: 0.10 kWh per m³
  3. Average power over the running time: 9.48 kW
  4. Energy used in a year: 23700.00 kWh
  5. Running cost for the year: $5925.00
  6. Cost of 1000 m³ of free air: $28.50 per 1000 m³
  7. Yearly cost of the air lost to leaks: $1050.00
  8. Saving from a lower set pressure (rule of thumb, about 7 % per bar): $207.38 a year

Change the numbers in the calculator to see the full working, every step, for your own case.

Common questions

What does the kW on the controller mean?

On many controllers the POWER reading is the motor input power the controller calculates. It reads high while the machine is building pressure after a start, so take it once the machine is loaded and the pressure has settled.

What is a good specific power for a screw compressor?

Around 6 to 7.5 kW per m³/min of free air at about 7 bar for fixed-speed oil-injected machines. Variable-speed machines can do better at part load.

Why are leaks so expensive?

Leaked air has been compressed and paid for. A compressor must run to replace it all day, including when no tools are in use.

Does lowering the pressure really save energy?

Yes. A common rule of thumb is about 7 percent of compressor power for every bar of set pressure, as long as your tools still get the pressure they need after line losses.

Related calculators

Got a question about this? Ask an engineering question and get a plain-language answer with references.

Further reading: Compressed air system guides from compressor manufacturers and energy-efficiency agencies.

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