Compressed air is often called the fourth utility of the workshop, after electricity, gas and water. It is also one of the most expensive, because producing it takes a lot of electricity. Knowing the price of a cubic metre lets you put a figure on a leak, compare two compressors or justify an investment.
The formula in two steps
Step 1: the energy to produce 1 m³
Divide the compressor's power by the volume of air it produces in an hour:
kWh per m³ = power (kW) ÷ (air flow in m³/min × 60)
The result is called the compressor's specific power. The lower it is, the more efficient the machine.
Step 2: the price per m³
Then multiply by the price per kWh your business pays:
€ per m³ = kWh per m³ × price per kWh
An example with a screw compressor
Take the S 110: 11 kW, 1.7 m³/min at 8 bar, according to its data sheet. The price per kWh, here €0.20, is an assumption to replace with your own.
- Air produced in one hour: 1.7 × 60 = 102 m³.
- Energy per m³: 11 ÷ 102 ≈ 0.11 kWh/m³.
- Price per m³: 0.11 × 0.20 ≈ €0.02, or about €2 per 100 m³.
With the same calculation, at 8 bar and still based on motor power:
| Model | Power | Air flow at 8 bar | Energy per m³ |
|---|---|---|---|
| S 75 | 7.5 kW | 1.1 m³/min | about 0.11 kWh/m³ |
| S 110 | 11 kW | 1.7 m³/min | about 0.11 kWh/m³ |
| S 150 | 15 kW | 2.2 m³/min | about 0.11 kWh/m³ |
| S 220 PM | 22 kW | 3.6 m³/min | about 0.10 kWh/m³ |
These figures are a theoretical minimum: they are based on the motor's rated power, with the compressor loaded. The real cost is higher, for the reasons below.
What pushes up the real price per m³
1. Unloaded running
A fixed speed compressor running unloaded still uses a large share of its power, around a quarter, without producing air. Those kWh go on the bill without adding any m³. A variable speed compressor greatly reduces this: see variable speed or fixed speed.
2. Leaks
Air that leaks has been paid for like the rest. If part of the output goes into leaks, the price of each m³ actually used rises accordingly. The leak cost calculator shows what a leak costs you, and our article explains how to detect and repair leaks.
3. Pressure
The higher the pressure, the less air the compressor produces for the same power: on the S 110, air flow drops from 1.7 m³/min at 8 bar to 1.1 m³/min at 13 bar. A commonly quoted rule of thumb is about 7% more energy per extra bar. See 10, 13 or 16 bar compressor.
4. Air treatment and maintenance
The dryer also uses electricity, and every filter causes a small pressure drop. A clogged air filter or saturated separator makes the machine work harder for the same air flow: servicing on schedule keeps specific power as low as possible.
Measuring your real cost
To know your true price per m³, you need two figures over a given period:
- the electricity used by the compressor and dryer, read from a sub-meter or estimated with the electricity cost calculator, which takes loaded time into account;
- the air used by the workshop, measured with a flow meter.
Divide the cost of the electricity by the volume of air: you get your real price per m³, leaks and unloaded running included. This is what a compressed air audit measures, and it also shows where to act first.
Why this figure matters
Over a compressor's life, electricity weighs far more than the purchase price: our guide on what a compressor really costs explains this. Knowing the price per m³ lets you put a figure on every improvement (a leak repaired, pressure lowered, a better-sized machine) and check whether it pays off. Depending on your country, some of these improvements may qualify for energy efficiency grants.
For your trade: Compressor for industry and production, Compressor for plastics processing, Compressor for the food industry.