Air Compressor CFM & Tank

Adding up the plate ratings of every tool in a shop gives a number nobody needs: an impact wrench rated at 4.5 cfm runs in two-second bursts, perhaps a fifth of the time. Multiplying each tool by its duty cycle gives the average demand, which is what the compressor has to replace; the simultaneity factor then accounts for how much of that actually overlaps, and your margin covers leaks, wear and the next tool. The peak is still reported, because it is what the receiver has to cover.

A tank stores no extra air in the sense people expect — it buys time. The isothermal storage relation V = Q·t·p_atm ÷ (p₁ − p₂) says how big it must be to keep the motor within the starts per hour its maker allows, taking t as the worst-case quarter cycle. The same relation run backwards gives the hold-up: how many seconds an existing tank covers the demand across the pressure band, and how long the compressor takes to pump it back up with nothing drawing. A wider band, or a bigger tank, both mean fewer starts.

Free air delivery is at the standard conditions your supplier states; this page does not convert ACFM to SCFM, and displacement is not delivery — a piston machine delivers roughly 60 to 80 per cent of its swept volume. Pipe pressure drop, altitude, intake temperature, moisture and dryer losses are all outside the calculation. Tool consumptions are yours from the tool’s plate, since makers quote them at different pressures and duty cycles and a stored table would mislead. Nothing leaves the browser; the same four anonymous usage counts as the rest of the site apply.