If you have an impact wrench or you’re looking to purchase one for a project at home or in the workshop, you may now be wondering what size air compressor you need to run your impact wrench.

This page will serve as a guide into what size air compressor you need for your impact wrench!

Table of Contents

Key Considerations – Choosing an Air Compressor for an Impact Wrench

There a a few very key considerations you must look at when finding an air compressor suitable for an impact wrench. These are:

  • Use cycle – Continuous vs Intermittent Use
  • CFM requirements & CFM rating of the impact wrench
  • Pressure requirements of the impact wrench
  • Duty Cycle of the air compressor
  • CFM delivery capability of the air compressor
  • Air compressor tank size (compressed air storage capacity)
  • Distance you’ll be using the impact wrench from the compressor (hose length)

Are You Using the Impact Wrench Intermittently or Continuously?

The first thing you must consider is whether you require require continuous or intermittent use out of your compressor for your impact wrenches work.

If you only require intermittent use of your impact wrench then a small compressor may suffice but if you require continuous use then the compressor has to have the discharge capacity that the impact wrenches demands.

A typical use cycle on an impact wrench in a non-assembly line environment is likely to be far less than 50% of the time drawing it’s full CFM rating.

What CFM Rating Impact Wrench Have You Bought or Are You Considering Buying?

Impact wrenches come with CFM ratings, often expressed as SCFM ratings (as it’s a standardized unit). This can also be expressed as “Air Consumption”.

Example of a Small Impact Wrench

Here’s an example of a small impact wrench, the Chicago Pneumatic 3/8″ drive 200 ft-lbs torque output impact wrench which is rated at an average consumption of 3.8 CFM.

  • Drive size: 3/8″
  • Torque: 200ft-lbs
  • CFM: 3.8

Example of a Medium Impact Wrench

This 1/2 inch 500ft-lbs pneumatic impact wrench by jet jat is a medium offering that has a 5 CFM average air consumption according to its manual.

  • Drive size: 1/2″
  • Torque: 500ft-lbs
  • CFM: 5

Example of a Large Impact Wrench

Here’s an example of a 1/2″ drive 900 ft-lbs larger impact wrench. It’s rated at an air consumption of 8 CFM as per the manufacturer’s rating.

  • Drive size: 1/2″
  • Torque: 900ft-lbs
  • CFM: 8

What Pressure Rating Impact Wrench Have You Bought or Are You Considering Buying?

All air tools, air impact wrenches being no exception have a recommended operating pressure.

The Aircat 1150 as an example has a stated recommended operating pressure of 90 PSI. This is a commonly recommended pressure for many air tools.

The Jet-Jat-107 also states a recommended tool pressure of 90 PSI. Their tools operate on 70-100 PSI but strongly recommends against pressures in excess of 100 psi as that will shorten the tools life.

Whilst the Chicago Pneumatic’s impact wrench manual states that it has a maximum working pressure of 90 PSI.

Air Compressor Duty Cycle

The typical duty cycle of an air compressor is 50% as can be seen in this Craftsman 919 manual. It states that the maximum compressor pumping time per hour is 30 minutes.

If you want to know more about air compressor duty cycles, how they’re expressed and calculated, you should read my article on air compressor duty cycles.

Here’s another example of a product manual which describes the duty cycle of a compressor in these terms:

“INTERMITTENT DUTY FORMULA

Pump-up time should not ordinarily exceed thirty (30) minutes or be less than ten (10) minutes. Shutdown periods between cycles of operation should be at least equal to the pump-up time. Note: When the compressor is regulated by constant speed control, the shutdown period is the time the compressor is operating unloaded.

This basically describes a 50% Duty Cycle.

CFM Delivery Capability of the Air Compressor

CFM ratings of air compressors tend to be based on the output of the air compressor pump.

However, to understand what ability the air compressor has to deliver CFM continuously you need to multiply the CFM rating by the Duty Cyle percentage.

So an Air Compressor CFM rating of 8 CFM with a 50% Duty Cycle would have the ability to deliver:

8 CFM * 50% = 4 CFM

Example of an Air Compressor Suitable for a Small Impact Wrench

Here’s an example of an air compressor which delivers 2.4 CFM – and the product manual describes what would be determined as a 50% duty cycle. Therefore the compressor would actually deliver 1.2 CFM (2.4 CFM * 50%).

This would be suitable for a small impact wrench given that you only require intermittent use. But, this compressor wouldn’t be suitable for continuous use on any of the impact wrenches presented in this article.

The small Chicago Pneumatic impact wrench requires 4 CFM, if the use was intermittent and only needed 25% of the time (15 minutes per hour), then the wrench only requires 1 CFM (4 * 25%). Therefore, this compressor would be capable of providing that that CFM.

However, if you required to use the impact wrench on a 50% duty cycle, the wrench would require 2 CFM (4 * 50%). The air compressor running at it’s recommended 50% duty cycle would not be able to provide the amount of CFM required by the impact wrench.

It would only be able to provide the 2 CFM requirement if you overworked the compressor by running it on a 90-100% duty cycle which is strongly not recommended.

Example of an Air Compressor Suitable for a Medium Impact Wrench

Here’s an example of an air compressor which is rated 5.30 CFM – and though product manual does not describes the duty cycle, a customer Q&A response has declared that the compressor has a 70/30 (70%) duty cycle. What would be determined as 20-25 minutes rest after each hours use.

Therefore, this air compressor is actually capable of delivering 3.71 CFM (5.3 * 70%). This is slightly undersized for continuous use of the 3.8 CFM Chicago Pneumatic impact wrench or anything greater than that.

However, if the impact wrench only required being used intermittently (50% of the time) then this compressor is suitable for not only the Chicago Pneumatic impact wrench but also the medium Jet Jat impact wrench (5 CFM * 50% = 2.5 CFM).

If you were to obtain an impact wrench with a CFM of below 3.71 CFM then this compressor would be capable of delivering continuous use to that tool.

Example of a Large Air Compressor Suitable for Large Impact Wrenches

Here’s an example of a large Air compressor, the Ingersoll-Rand 8 Gallon twin compressor capable of delivering 11.5 CFM with 100% continuous duty cycle.

This compressor is suitable for providing continuous use to the small, medium or large impact wrenches provided. It could even power both the small Chicago Pneumatic and medium Jet Jat impact wrenches simultaneously.

If this compressor were to have a 50% duty cycle and therefore provide 5.75 CFM (11.5 * 50%) it would still be able to power the small or medium impact wrenches continuously.

It would consequently no longer be able to provide continuous use to the large impact wrench when working with a 50% duty cycle, but instead could work intermittently if the Air-Cat tool required 4 CFM (8 * 50%).

Example of an Extra Large Air Compressor Suitable for Powering Multiple Impact Wrench’s Simultaneously

Here’s an example of an industrial air compressor which delivers 38 CFM – and the product manual describes what would be determined as a 100% duty cycle.

This is a stationary compressor, that has a continuous run & automatic stop/start feature making it capable of powering small, medium and large impact wrenches continuously and even multiple at once!!

Air Compressor Tank Size (Compressed Air Storage Capacity)

Tank size will determine how much air is available to be drawn down at any time. This is also a key enabler in keeping a compressor within it’s duty cycle.

Therefore an 8 CFM compressor with a 50% Duty Cycle can be used to run an air impact wrench that’s rated at 8 CFM – if used intermittently with a sufficiently large air tank.

To keep a compressor running for at least 10 minutes with an impact wrench consuming 8 Cubic Feet of air per minute for 50% of the time, the storage capacity would be:

8 CFM * 10 minutes * 50% = 40 Cubic Feet of air (at atmospheric pressure (15PSI))

As atmospheric pressure is 15 PSI and the output pressure is 90 PSI and pressure and volume are inversely proportional 15 PSI / 90 PSI = 6

Therefore, you need 1/6th the volume of air at 90 PSI

40 Cubic Feet * 1/6th = 6.6 Cubic Feet

6.6 Cubic Feet = 187 Litres

This is to give you a basic idea on the capacity needed based on the Ingersoll Rand impact wrench’s (presented earlier) minimum running time.

Distance You’ll be Using the Impact Wrench From the Compressor (Hose Length)

Long hoses will result in pressure drop. The AIRCAT 1150 manual recommends that a compensation for pressure drop should be made if the hose is over 25 feet long.

The JET-JAT-107 manual states that the hose should be just long enough to serve the working area.

For further information on air hoses visit our Air Compressor Hose & Tube Guide.

Reader Questions and Responses

Question:
by Ken
(Abbotsford, BC, Canada)

Hi Bill. Great site, just discovered it.

I own a CH portable oil lubricated 8 gallon compressor, output is 3.7 cfm @90 psi. Bought it used when all I wanted was compressed air for automotive parts cleaning and the like. It happened to come with the crappy, 250 ft/lb impact wrench (rated at a relatively high 5.4 cfm) which is useful for tire removal and I do find myself using it for other things but it is limited.

Impact wrench - this one is made by Ingersoll Rand
Impact wrench – this one is made by Ingersoll Rand

I now find myself looking for a more powerful wrench and find that most of the higher grade units demand even less cfm and deliver more torque than the one I have. My present wrench appears to be working at 100% capacity and, given the gap between the cfm rating of this tool and the compressor, it appears that one can get away with it in the case of intermittent use??

My theory is that the tool will receive it’s rated cfm and perform at 100 percent until tank pressure drops below 90 psi? Is this correct?

Could you say that compressor rating seems to be a factor only when the pump kicks in and is expected to deliver air to a running tool (at which point you will likely be done using the tool for that cycle of usage)?

Do you think I could get away with a better wrench and expect 100% efficiency when supplied by this compressor?

I did upgrade to 3/8″ hose some time ago but didn’t change the stock 1/4″ fittings at the time. I recently changed to 3/8” fittings which I would expect are necessary to obtain the

full benefit of the 3/8” hose? Sorry for the wordy message but any information you might provide would be helpful.Thanks,
Ken

Response:

Ken, good to hear from you.

Many questions, all of which are answered on the various pages of this site and it makes no sense to retype all that information again here, sorry.

Specifically though, if you wish to run an air tool continuously, then the compressor has to have the discharge capacity that the air tool demands and if you wish to run the air tool in a production facility, the compressor also have a duty cycle to withstand the demand of that frequent or continuous run time.

If you have a tank full of compressed air and a small air compressor, your air tool will run fine until the reservoir of pre-compressed air is used up. Then, since the air compressor cannot deliver air as fast as the air tool consumes it, the available pressure and flow will decrease to the point where the air tool cannot operate.

At that point you must stop using the tool and wait for the tank to refill.

If your air compressor is small and you want to use a higher demand air tool, you run the risk of burning out your compressor depending on it’s duty cycle.

As far as I am concerned, the small air compressor is good for blowing off work benches and operating tools that have intermittent air use, such as brad nailers and the like.

If you need to work with a high demand air tool like the impact wrench, and you need to do a lot of work, you want to move up to a 3HP + air compressor, and if your livelihood depends on using air, at least a 5 HP with a 60 gallon tank.

See the sitemap page for links to pages with more specific info.


If you have any questions regarding what size air compressor you need for an impact wrench, please leave a comment below with a photo if applicable so that someone can help you!