SCFM To ACFM Calculator: Convert SCFM To ACFM (+ Formula)

Air compressors, for example, are rated in SCFM (Standard Cubic Feet Per Minute). In many cases, we will have to convert SCFM to ACFM (Actual Cubic Feet Per Minute). The conversion to ACFM (based on actual pressure, temperature, and relative humidity) will give us an idea of what airflow an air compressor can actually produce in real-world conditions.

air compressor scfm to acfm conversion
500 SCFM air compressor won’t produce 500 CFM of airflow in practical use. We have to calculate ACFM in order to determine the airflow we will get at real-world conditions.

Standard CFM to Actual CFM is one of the more complex conversions, but don’t worry; we’ll guide you every step of the way. We will take a structured approach here so we don’t get lost in all these pressures (PSI), and temperatures (°R and °F). To help everybody out, we have created the following 2 tools you can freely use:

  1. SCFM To ACFM Calculator. Here, you insert a bunch of actual condition metrics (SCFM, Pstd, Pact, Psat, Relative Humidity (Φ), Tact, and Tstd, and you get the ACFM equivalent. Example: 100 SCFM is equal to 118.01 ACFM at 14.7 PSI standard pressure, 13 PSI actual pressure, 0.6 PSI saturated pressure, 68°F actual temperature, 60.33°F standard temperature, and 60% relative humidity.
  2. SCFM To ACFM Formula. We look at the original formula (ACFM = SCFM × (Pstd/(Pact – Psat × Φ)) × Tact/Tstd) and show you how to simplify it (using standard conditions, setting relative humidity to 0% to avoid calculating saturated pressure, etc).

We will start with the calculator. Now, there are many inputs here (don’t get scared off). In the 2nd section (SCFM to ACFM formula), we will look at how we can simplify or omit some of these inputs to make the conversion much easier. Here is the SCFM to ACFM online calculator:

Let’s have a look at 1st example just to illustrate how this calculator works:

Say you have a 300 SCFM-rated airflow at standard conditions (14.7 PSI standard pressure, 60.33°F standard temperature (equal to 520°R or degrees Rankine), and non-standard 50% relative humidity). The measured pressure is 12.2 PSI (about 5000 ft elevation), and the measured temperature is 80°F. How many ACFM do we get from 300 SCFM-rated airflow?

You can insert ‘300’ in the 1st SCFM field, ‘14.7’ in the 2nd standard pressure field, and ‘12.2′ in the 3rd actual pressure field. For the 4th field input – saturated pressure – you need to use this water saturation pressure calculator – we see that saturated pressure at 80°F is 0.51 PSI, and we thus insert ‘0.51’ in the 4th field. We then proceed to insert actual and standard temperatures, as well as 50% relative humidity. Here is the result we get (screenshot):

converting scfm to acfm with an online calculator

We can see that, at these conditions, 300 SCFM is equal to 383.16 ACFM. If you need this conversion in reverse – ACFM to SCFM – you can check out a similar ACFM to SCFM calculator and formula here.

Why do we have to insert so many different metrics for this conversion (and how to omit some of them)? Let’s have a look at the SCFM to ACFM formula to see why all these pressures and temperatures matter:

SCFM To ACFM Formula

The difference between SCFM and ACFM is that standard CFMs are measured at standard theoretical conditions (14.7 PSI, 520°R, and 0% relative humidity in the US), while actual CFMs are the airflow we actually get in the real world.

This is the equation that converts SCFM to ACFM (notice all these metrics we had to insert in the calculator above):

ACFM = SCFM × (Pstd/(Pact – Psat × Φ)) × Tact/Tstd

Here’s what these abbreviations in the SCFM to ACFM formula mean:

  • Pstd is standard absolute pressure. This is usually sea-level 14.7 PSI pressure.
  • Pact is actual absolute pressure, expressed in PSI.
  • Psat is saturation pressure at actual temperature (Tact), expressed in PSI. We use the water saturation calculator here to determine the PSIs at certain temperature.
  • Φ is the actual relative humidity. Example: At 60% relative humidity, we insert 0.6 in the equation.
  • Tact is actual ambient temperature, expressed in degrees Rankine (°R).
  • Tstd is standard temperature, expressed in degrees Rankine (°R). We take 520°R as the standard temperature (equal to 60.33°F or 5.74°C).

Now, we can simplify this equation a bit. You might notice that if the relative humidity is 0%, the product Psat × Φ in the formula will always be 0 (regardless of Psat; which means we don’t need to calculate saturated pressure).

The simplified SCFM to ACFM equation at 0% relative humidity looks like this:

ACFM = SCFM × Pstd/(Pact) × Tact/Tstd

Now this seems a bit more manageable. Let’s solve another example using the European standard conditions:

Say we want to convert 100 SCFM at European standard conditions (1 atm pressure (14.7 PSI), 0°C (32°F or 491.67°R), and 0% relative humidity). The actual conditions include 13.4 PSI pressure and 25°C temperature (equal to 77°F or 536.67°R). Let’s insert all these numbers in the 2nd simplified equation:

ACFM = 100 SCFM × 14.7 PSI/(13.4 PSI) × 536.7°R/491.67°R = 131.52 ACFM 

We can see that 100 SCFM (at these actual conditions) is equal to 131.52 ACFM. You can use the calculator above to check this; notice that once you set relative humidity to 0%, you can insert anything for saturated pressure, and the resulting ACFMs won’t change.

Note 1: Since degrees Rankine used in the formula are less known, you can help yourself with Rankine to Fahrenheit (°R to °F) conversion here, and Fahrenheit to Rankine (°F to °R) conversion here.

Note 2: The resulting ACFM is not equal to CFM. You can read about the difference between SCFM and CFM and the conversion between them here.

Hopefully, by using the formula, or, more easily, using the SCFM to ACFM calculator, you now have 2 tools to make this conversion. If you need a bit of help from us, you can always use the comment section below, give us a few metrics, and we can do some math together.

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