What Size Air Compressor Do I Need?

Know your tools’ cfm and psi requirements to select a compressor.

Many projects would sputter to a halt without air compressors to drive pneumatic tools. But it’s not always obvious what size air compressor is required for the job, and it’s easy to err on the side of too large or too small. Here are a few things you should consider in making your selection.  

Know your airflow (cfm)

Pneumatic tools are rated with two important criteria: the airflow they require and the operating pressure they’re designed to accommodate. 

Let’s start with airflow. This rating, measured in cubic feet per minute (cfm), is how you match the compressor to your tools to ensure that the compressor can deliver enough airflow for the tool to do its job. You’ll find the cfm requirements on the tool’s label or in the user guide. Airflow needs vary greatly; a small tool like an air nailer might require only 1 to 2 cfm, while a pavement breaker needs 90 cfm or more, and some heavy-duty tools need hundreds of cfm. 

The math for figuring out your compressor’s ideal cfm is simple: If your compressor will be powering only one tool at a time, find the cfm requirements of all the tools you plan to use, choose the highest cmf, then multiply it by a safety factor of 1,5 (because the cfm will drop as the pressure in the compressor’s tank drops). This is the size of compressor you need, and it includes a buffer to allow you to continue working even as the pressure in the tank drops while the tool runs.

If you plan to run multiple tools from the same compressor at the same time, calculate the compressor you need by adding up the cfm of all the tools you plan to use, then multiply the total by 1,5. Be sure the compressor you’re considering is designed to power all the tools you plan to use. Light-duty compressors may be rated only for single tools, while heavier-duty compressors come ready for multi-tool duty with multiple outlets. 

A huge range of compressors exists, from a compact electric 3 to 5 cfm compressor with built-in wheels, small enough for a single person to wheel around the worksite (and handy for filling tires) to a diesel powered 16 000 to 18 000 cfm compressor built onto a towable trailer. The airflow of the compressor will vary based on what you set the pressure (PSI) at, so when you compare models, compare the cfm at the same PSI.

Typical cfm of common tools

The chart below indicates the average typical cfm requirement of common air tools.

Air ToolCfm Requirement
Tire inflator2
1/2-inch drill4
Air hammer4
Coupeuse plasma5
Meuleuse d'angles6
Ponceuse orbitale6
3/4-inch impact wrench7
Meuleuse à filière8
Gravity feed spray gun18
Disc sander20
90-pound paving breaker90
Sand blaster20-250

Get as close as you can to matching the total cfm requirements of the tools to the compressor. For example, you could efficiently run a pair of 60-pound paving breakers off a 175 to 195 cfm compressor, but if the only thing you connect to the compressor is a single 90-pound paving breaker, you’ll be wasting fuel. 

Know your pressure (psi) 

Another factor to consider is the compressor’s pressure, measured in pounds per square inch (psi). Smaller compressors tend to be rated for 90 psi, while heavier-duty compressors may be rated for 150 psi or higher. 

You can damage tools by using too much air pressure, so match the pressure rating of the tool to the compressor. 

Consider the tank size

Pneumatic tools run off stored, pressurized air, so the tank size determines how long your tools can run before the compressor motor has to turn back on to re-pressurize the air. Larger tanks don’t have to run as often to maintain pressure. You can find compressors with a very wide range of tank sizes, from 2 gallons to 80 gallons. Of course, larger tanks take up more space.

For tools that require continuous air flow, such as grinders and sand blasters, you’ll want a large tank; otherwise, you’ll need to stop working more frequently to let the compressor top off the tank and cool off. For tools that require quick bursts of air, you can get by with a smaller tank. 

It goes without saying that you should have the proper training and experience necessary to operate a compressor. Furthermore, you should consult with an expert about the particulars of your job and you should adhere to all manufacturer specifications regarding the use and operation of any compressor and/or accessories that you are employing for your job. 

United Rentals carries a wide variety of compressors and accessories.  To inquire as to the availability of compressors and accessories for your next project, contact a United Rentals sales representative at a branch near you or call 1-833-480-0609.

Dave Johnson is a Los Angeles-based freelance writer who has been writing about all aspects of business and technology since before there was an internet. 

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