Air Compressor Size Calculator

For a typical fleet workshop using a ½″ impact wrench and tyre inflation one tool at a time, you need a minimum of 5–6 CFM (140–170 L/min FAD) and a 50–100 litre tank. If you also use a die grinder or air chisel, budget for at least 7–8 CFM (200–230 L/min). Oil-lubricated compressors are recommended as they run cooler, last longer and cope better with continuous sessions.

CFM (Cubic Feet per Minute) is the flow rate — how much air the compressor actually produces per minute. Tank size is just the reserve. A large tank with a low-CFM compressor will eventually drain and be unable to keep up with a continuous-use tool. UK compressors often quote FAD (Free Air Delivery) in litres per minute — 1 CFM = 28.3 L/min.

Swept volume ("displacement") is the theoretical maximum output of the pump — always higher than actual. FAD (Free Air Delivery) is the actual measured output at the outlet at a stated pressure. Always compare compressors using FAD, not swept volume.

Inflating a plant or heavy vehicle tyre requires approximately 5 CFM (140 L/min) at 90 PSI to fill at a reasonable rate. Large trailer tyres can need 8 CFM or more. Tyre inflation is intermittent, so a large tank helps significantly.

For fleet workshop use, oil-lubricated is almost always the better choice — it runs cooler, lasts longer, is quieter and handles longer duty cycles. Oil-free is fine for light, occasional use such as tyre inflation. For regular impact wrench, grinding or continuous tools, choose oil-lubricated.

Up to about 3.7 kW (5 HP) is typically achievable on a 32A single-phase supply, covering most workshop compressors up to around 14–16 CFM. Above that, 3-phase is usually required. Check your supply before buying.