Many projects would sputter to a halt without air compressors to drive pneumatic tools, but it’s not always obvious what size air compressor you need. It’s easy to err on the side of too large or too small. Here are a few things to consider when looking at different air compressor sizes.

Know your airflow: CFM for air tools

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 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 manual.

Airflow needs vary greatly. A small tool like an air nailer may require only 1 to 2 CFM, while a pavement breaker needs 90 CFM or more, and some heavy-duty air tools need hundreds of CFM.

Know your pressure: How much PSI do I need?

Air pressure is measured in pounds per square inch, or PSI. Compressors for smaller jobs are 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.

How to calculate CFM requirements for air tools

The math for figuring out your 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 CFM, then multiply it by a safety factor of 1.5. 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: Add 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 can handle multi-tool duty, and they provide multiple outlets.

Air compressors come in many sizes. A compact electric 3 to 5 CFM compressor with built-in wheels is small enough for a single person to wheel around the worksite and handy for filling tires. Medium-duty 30 to 45 CFM compressors can efficiently run multiple tools and pieces of equipment. At the high end is a diesel powered 16,000 to 18,000 CFM compressor built onto a towable trailer.

The airflow of the compressor will vary based on the PSI setting.

CFM Requirements for Common Air Tools

The chart below indicates typical air tool CFM requirements at the most common PSI setting. When you compare models, always compare the CFM at the same PSI. Some tools are listed with a wide range of CFMs because they are available in light to heavy-duty models.

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.

Tank size: How big of an air compressor do I need?

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 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 re-pressurize and cool off. For tools that require quick bursts of air, you can get by with a smaller tank.

No matter what size compressor you’re using, wear the proper PPE and follow all manufacturer guidelines on safe operation.

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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