Air compressor CFM per HP

Here is every compressor in our registry that publishes both a horsepower figure and a CFM at 90 PSI figure, with the ratio worked out. Note how many makers publish one and not the other - Bostitch and Metabo HPT publish no horsepower at all for the machines listed, and WEN publishes a motor amperage instead.

The pattern worth seeing: the two highest ratios belong to 6-gallon oil-free pancakes at 0.8 and 0.9 HP delivering 2.6 CFM. The lowest belong to 20-gallon oil-free machines at 1.3 and 1.8 HP delivering 4.0. A buyer reasoning from horsepower would conclude the 20-gallon machines are more capable by a wide margin. On CFM they are more capable by 54%, not by the 125% their horsepower implies.

The DEWALT DXCMLA1983054 is the most instructive entry. At 1.9 published HP it delivers 5.7 CFM at 90 PSI - a ratio of 3.0 - from a cast-iron twin-cylinder oil-lubricated pump on a belt drive. The Craftsman 20-gallon at 1.8 HP delivers 4.0 CFM from an oil-free direct-drive pump, a ratio of 2.2. Nearly the same motor, 43% more air, because the pump is better.

And the Metabo HPT EC914S shows why the whole exercise is secondary: it publishes no horsepower figure whatsoever and delivers 4.0 CFM at 90 PSI with a 200 PSI ceiling. You can buy it confidently on the strength of a number it does publish.

Four things sit between the motor nameplate and the air at your coupler, and they explain the whole spread in that table.

Pump design first. A cast-iron twin-cylinder pump turning slowly on a belt drive is a more efficient air pump than a fast aluminum single turning on a direct drive, and it rejects heat better. That is the DEWALT-versus-Craftsman comparison above: nearly identical horsepower, 43% more air, because one is a better pump.

Drive type second. A direct-drive pump turns at motor speed, which means fast, hot and noisy; a belt drive lets the designer choose the pump speed independently. Slow is efficient and quiet and long-lived, which is why belt-driven machines publish better ratios and why the quiet-series machines pay for their silence in output rather than in horsepower.

Cooling third, which is the hidden one. Compressing air makes heat, and a hot pump is a less efficient pump. Cast iron, a real cooling fan and an intercooler tube between stages all keep the pump closer to its design point for longer, which shows up as sustained output rather than headline output.

And duty cycle fourth. Two machines with the same CFM figure are not equal if one can only hold it for a few minutes. California Air Tools publishes 70/30 for the 10020C and a 30-to-60-minute maximum continuous running time for the 8010A - real statements most of this category will not make. A machine with a good ratio and no duty statement is making a promise it has not quantified.

Turn the question round. Do not ask how much horsepower you need - ask how much CFM your tools demand at 90 PSI, then buy the cheapest machine that publishes more than that with margin, and let its horsepower be whatever it is.

Work the demand out from the tools, not from the compressor. The table below is every tool class with its published consumption and its duty behavior. Add up what you will realistically run at the same time - which for a one-person garage is one tool - and then add margin, because published averages for burst tools generally assume a duty factor. The Engineering ToolBox table states its own basis plainly: the ratings are computed at a 25% load factor, and full continuous performance needs four times the stated volume.

There is one place where horsepower does tell you something real, and it is about the circuit rather than the air. A 15-amp 120V household circuit caps a motor at roughly 1.5 to 2 running horsepower, which caps delivered air near 5 to 6 CFM at 90 PSI. So if a machine claims more than 2 running HP on a household plug, read the fine print - it is either a peak figure or it needs 240V. The DEWALT at 1.9 HP and 5.7 CFM sits right at the top of what 120V can honestly do.

That is the useful way to use horsepower: as a sanity check on whether a listing is lying to you, not as a shopping criterion.

Four patterns worth recognising, because once you see them you stop being sold by them.

Peak horsepower as the headline. Senco publishes 0.5 running against 1.0 peak; California Air Tools publishes 1.0 against 2.0. If a listing shows a single large horsepower figure with no qualifier, assume it is peak and halve it mentally. A maker confident in its machine publishes running HP and CFM at 90 PSI.

CFM quoted at 40 PSI instead of 90. Output rises as pressure falls, so 40 PSI always looks better. The DEWALT DXCMLA1983054 publishes 5.7 CFM at 90 and 7.0 at 40; the Husky C201H publishes 4.0 and 5.2. Both are honest because both numbers are given. A listing quoting only a 40 PSI figure is choosing the flattering one.

Tank gallons used as a capability claim. Gallons are storage, not output - the pump makes the air. A 20-gallon machine at 4.0 CFM makes less air than a 10-gallon machine at 5.3, and the 20-gallon one simply takes longer to run out.

And silence where a number should be. No published CFM at 90 PSI, no published dBA, no duty-cycle statement - each omission is information. We note the gaps rather than filling them, which is why several cells in the table above read Not published rather than carrying an estimate.