Compressor Sizing Calculator

Sizing a compressor from a simple sum of every tool's rated air demand almost always over-buys, because tools rarely all run at once — this calculator applies a diversity factor to your total CFM demand to reflect how much of that demand is realistically simultaneous. It then layers on an altitude correction (roughly 3% more CFM needed for every 1,000 ft of elevation, since thinner air means the compressor must move more volume to deliver the same mass of air) and a safety margin for future growth and system losses, arriving at the required compressor CFM. From there, required horsepower is estimated using an approximate CFM-per-horsepower relationship that declines slightly as operating pressure rises (roughly 6.5 minus 0.02 times the pressure in psig, floored at 2) — a simplified stand-in for the real efficiency curves that vary by compressor design and manufacturer.

That HP figure is rounded up to the next size in a standard motor lineup (3 HP through 500 HP), since compressors aren't built in arbitrary increments, and electrical draw is derived assuming a 92% premium-efficiency motor. Finally, the calculator suggests a compressor type purely from required flow: under 30 CFM points to reciprocating, up to 1,500 CFM to rotary screw, and above that to centrifugal — a common rule of thumb, not an engineering specification. Because the CFM-per-HP and motor-efficiency figures are fixed approximations rather than data pulled from a specific manufacturer's cut sheet, treat the output as a solid starting point for a quote, not a final purchase spec.