It's not unusual for individuals to purchase the wrong size air compressor. Begin by performing a requirements analysis. Look at the air requirements of the tools that you'll be using. Specifically, focus on tool air consumption at load, not average air consumption. Most marketing literature focuses on "Average Air Consumption," which gives the appearance that most compressors will adequately drive the most common air tools. Reality ends up being something quite different.

For industrial clients, Ingersoll-Rand only quotes "Average Air Consumption at Load," not "Average Air Consumption." The differences can be huge, especially with impact wrenches. Take, for instance, Ingersoll-Rand's 231C impact wrench, the most popular 1/2-inch drive wrench in the world:

PMAX: 90 psi
Avg. Air Consumption: 4.2 cfm.
Avg Air Consumption@Load: 22 cfm.

Most homeowner-size compressors won't come close to meeting the 22 cfm avg. air consumption @ load requirement. Therefore, instead of getting 600 lb.-ft. of nut busting torque in reverse, they may only get 200 lb.-ft. That can make the difference between removing a rear axle nut to replace a wheel bearing or not. Most tool testing performance statistics assume a 15 foot (3/8-in. I.D.) hose, not the 25 to 50 foot hoses that most people use. Remember, every 10% drop in line pressure results in a 14% drop in tool power and an 11% drop in torque. Attaching an inexpensive pressure gauge to the end of the hose will give you a handle on line drop. Therefore, average air consumption at load and line drop become extremely important factors in selecting the proper size air compressor.