CFM for Impact Wrenches

An impact wrench is a powerful tool that can replace the functions of a hand wrench. Instead of tightening your lug nuts and bolts by hand, an impact wrench makes it easy to fix or remove wheel studs and bolts from vehicles and heavy machinery.

Automobile shops may have one or several types of wrenches depending on the scale of operation and activities. Yet, depending on the frequency of use, you may have a corded electric, cordless rechargeable battery or pneumatic impact wrenches.

Pneumatic wrenches are quite common and are less expensive compared to the other two. The amount of airflow from an air compressor to your pneumatic wrench is measured in cubic feet per minute (CFM). But, what is the size of your wrench?

Impact Wrench Sizes

A garage may have either depending on the bolt sizes and the difficulty of the job. Rusty lug nuts prove to be tough to remove. And you need an impact wrench with a higher torque force than that of the nut (at least 150 ft/lbs) to remove it. Here are the common sizes of impact wrenches.

1/4” impact wrenches

These are the smallest sizes available. They are common for use in enclosed and unreachable areas. They are also compatible with small tank air compressors.

3/8” and 1/2”

These two are the medium sizes that are common in auto-garages and most workshops for tasks a tire change bolts tightening. They have a minimum torque force of 250ft/lbs.

3/4″ and 1”

These wrenches are large and carry some weight. That’s why their air compressor tanks need support to provide stable output for heavy-duty jobs like on construction sites. They also cover a lot of area space and therefore need to have a particular station for the operations.

Now, do you have to worry about the CFM of your tool? Depending on the size of your impact wrench, you need to know how much airflow you need at a normal pressure of 90-100 psi. Well, it also determines the torque force. Several factors affect the CFM for an impact wrench.

More Read:

Top Cordless Rotary Hammer Drill

Top Cordless Drill Under $50

Factors That Determine the CFM of an Air Compressor

Airflow in a pneumatic wrench determines the speed of the motor. Since the speed is self-adjusting to deliver the rotations and impact, you need a good flow with constant pressure. Check out the following factors.

1. Diameter of the air hose

A larger diameter delivers more air to the impact wrench. For example, ½  inch impact wrench requires a diameter of 3/8. Compatibility depends on the inside diameter of the connectors, not the overall diameter.

2. Tank size

A larger tank provides more airflow with less waiting time unless it supports more than one tool. A small tank for example a 3-gallon on ½” impact wrench may not be enough compared to lighter tools like the nail gun.

3. Length of air hose

Air pressure drops with an increase in length. A small size air compressor may not need more than one connector, as this makes the end pressure much lower than at the source. A long air hose is also heavy and all this cuts the air pressure significantly.

4. Type of air hose

A normal standard air hose carries a higher air volume than a recoiling air hose. Apart from the keeping space, you should consider the effectiveness of air volume reaching the impact wrench. Hence, a standard air hose provides enough output to keep the machine stable.

How to Determine the CFM for an Impact Wrench

While observing all other causes of the shift in CFM, there is also a standard guide for the same.  A psi chart provides the CFM of all air tools against a standard pressure (70-100psi).

Besides that, it also depends on whether you are using a single-stage pump that has a maximum of 150 psi or a double-stage pump with a maximum of 175 psi. Higher air pressure makes the airflow stronger.

Depending on the size of the impact wrench, this is what our experts recommend.

¼” impact wrench- CFM of 1-1.5. This is necessary for light jobs that do not take much time.  Working with a 3-gallon tank may be economical in this case.

3/8-inch- You may need a 5-gallon tank to maintain this flow and airflow of 3 CFM.

½” impact wrench- Because of the heavy torque tasks it does, you need a CFM of 4 or 5 which is the equivalent of a 6-gallon tank size. You can connect it around the garage for various jobs.

¾ “ and  1” impact wrenches-. Because of their tank size limitation, they are not common unless if you buy them for heavy construction purposes. Their airflow is at 8 CFM and above.

Also Check:


The CFM of an impact wrench depends on its size. The higher the volume of air in cubic feet per minute the better and more stable your impact wrench. If you should invest in any type of wrench, remember that a pneumatic wrench is cheaper and easy to maintain. There is no better choice of a tool than one with the least maintenance expenses.

Leave a Comment