Any equipment that involves air compressing or heating and cooling air will usually measure their performance on either Standard Cubic Feet per Minute (SCFM) or Cubic Feet per Minute (CFM). Regardless of whether you are measuring in SCFM or CFM, the figure will relate to the amount of air that a device can provide. The SCFM or CFM score is important because this will tell you what tools you will be able to use with an individual air compressor, so it is important that you understand the difference and how it works!
However, with different machines using different systems to provide you with this information it can be difficult to know which is better to look for and also how to compare products that are using these different measurements. Our article aims to help…
What actually are SCFM and CFM?
Let’s start with CFM – Cubic Feet per Minute. This is the amount of air that can be provided, or “exchanged” depending on the pressure and the temperature that is needed by the machine that you are trying to power.
SCFM – Standard Cubic Feet per Minute – is slightly different. For this measurement, the manufacturers assume a standard temperature and pressure, and provide you with the cubic feet per minute of air that can be produced in these conditions. This is normally around 14.7 psi (atmospheric pressure) and 20℃ (room temperature).
NOTE: It is important to remember that there are different “standard” temperatures and pressures used around the world, which will make a difference if you are comparing products manufactured in different countries – so make sure to check this before purchasing!
SCFM vs. CFM
Originally air compressors, and other air producing machines, always measured their output in CFM at various pressures. However, this can make it very difficult to compare different products when it comes to purchasing them, as they could all be taking different pressures and temperatures into consideration!
However, although SCFM is a lot easier when looking at the figures on a product description, it is quite often a case of what you see isn’t necessarily what you get! The SCFM is usually worked out using standard atmospheric pressure and standard room temperature, but it is impossibly unlikely that the tool you are working with will be requesting these conditions! This can make it even more confusing to work out if the compressor is right for you (and the tools that you are wanting to use!).
When manufacturers advertise product information using CFM, they will usually do this considering a variety of pressures. This means that you will be able to look for the one that is the “closest fit” to the tool that you are going to be working with and see whether the tool is going to be right for you! Although equally, this doesn’t tend to take into account “real world factors” such as changes in humidity and air density, for example, which will also have an impact on the way your air compressor can work! There are a number of additional reasons why your air compressor may work at a lesser flow rate (CFM) such as heat, friction and blockages – none of which are taken into consideration with CFM.
TOP TIP: Remember when looking in the CFM offered with compressors, or other machines, that the PSI it is working at will not have a massive impact on the CFM. So, for example, if the CFM on the product description is when working at 90 PSI, but you only need 80 PSI, this won’t offer you massively more CFM with your air flow.
Although SCFM is looking at “idealistic” conditions, it is more honest in this, using the standard agreed conditions set by (usually) mechanical engineering bodies. This means that, yes, you will have to consider how the air flow will change depending on the conditions that you are working in, but this is easier to do when comparing it to the set conditions that it is giving as an example on the product description. It is also worth remembering that tools offering their product details in CFM are not going to be testing their compressors in disadvantageous conditions (or this is very unlikely!) as this would stop the machine from looking as appealing next to the competition. So machines offering their calculations CFM need to be looked at in more detail to make sure that they are all they say they are!
Main Thing To Remember
Unfortunately there are flaws to both the ways in which CFM and SCFM are measured, and we feel this is the most important thing that you need to remember when considering an air compressor, heater, or other tool that is measuring its “performance” in this way.
If it is being judged in CFM then remember to look at the different values it is offering at different conditions and PSI. If measured in SCFM then check to see which standard it is being judged/measured against, and compare this to the conditions that you are going to be working in most regularly.
Frequently Asked Questions
Is there a way to convert CFM to SCFM?
Yes, there is, but this does require some quite complex mathematical reasoning! There are numerous converting systems that you will find online so we would recommend using one of these to do the hard work for you!
How does Litres Per Minute link to Cubic Feet per Minute and Standard Cubic Feet per Minute?
This is purely a link between a metric and imperial system. Litres per minute is essentially the same as cubic feet per minute, just in a different type of system!
How can I work out with CFM I need for my tool?
We would recommend opting for a compressor that has a CFM 1.5 times higher than what you need for your tool. This means that you are giving the CFM rating of your compressor the benefit of the doubt by allowing for changes in conditions such as temperature.