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Q. I just built a 40 ft. x 60 ft. shop for automotive restoration and repair. I installed a new two-stage 5 HP air compressor that produces 19 cfm @ 100 psi. At times there could be three people working in the shop, using an assortment of air tools. How do I choose the size of my air lines?

A. Choosing the correct line diameter is based on your compressor’s cfm (cubic feet per minute) output rating, and how much flow is required to adequately supply all of the air tools simultaneously in use. Additionally, flow rates diminish as the line’s length increases; the longer the runs are, the larger diameter line you will need.

There are two ways to run air lines. Single-run systems have an individual air line from the compressor to the farthest point of use. Looped systems go all the way around the shop using a tee fitting at the compressor (or regulator/filter). This lets air travel in two directions, which balances airflow and doubles flow capacity.

Single-user shops or home garages typically will not require a looped system.

Use the charts below to determine the diameter line required for your application; round up in diameter size.


Air Tools Estimated Air Consumption

ToolAir ConsumptionToolAir Consumption
1/4" Die Grinder4 - 5 cfmRatchet4 - 5 cfm
Drill4 - 5 cfmBlow Gun2 - 3 cfm
3/8" Impact Wrench3 - 4 cfmAir Hammer4 - 5 cfm
1/2" Impact Wrench4 - 5 cfmOrbital Sander 6 - 9 cfm

Air Tool CFM Flow Chart

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Author: Dave Matthews

Dave Matthews was a mechanic for the U.S. Army, a Ford dealership, and served for many years as a fleet mechanic for construction companies. Now a technical content producer at Summit Racing, Dave has spent decades working on everything from military vehicles to high performance race machines.