Air Compressor Sizing: How Much Is Enough for Your Workshop?

An air compressor is sized by the air your tools actually breathe — measured in litres per minute or CFM — not by horsepower on the badge. Start by listing every air tool that might run at the same time and adding their consumption.

The sizing rules that matter

Add about 30 percent headroom to your total: compressors should not run flat out all day, leaks always exist, and shops always grow. Then look at the duty cycle. Piston compressors want rest — around half on, half off — making them right for garages and intermittent tools. Screw compressors are built to run continuously and reward steady demand with lower energy cost per litre, which is why factories standardise on them.

Tank size and buying used

The tank smooths bursts of demand: bigger tanks mean fewer motor starts and steadier pressure for spray guns and sandblasting. When buying used, drain the tank and look at what comes out — clean water is normal, rusty sludge means the tank was never drained and its life is shortened. On screw machines, ask for the service hours and when the air-end was last overhauled; that single part is most of the machine's value.

Right-sized, a good used compressor is one of the cheapest workhorses in the building — and one of the first things visitors hear if you got it wrong.