ACFM To SCFM: Convert ACFM To SCFM (With Formula)

If you need to convert ACFM to SCFM, you are in the right place. This is a notoriously difficult conversion; we want to calculate how many Standard Cubic Feet Per Minute (SCFM) we get from certain Actual Cubic Feet Per Minute (ACFM) at certain pressure, temperature, and relative humidity conditions.

Basically, in the real world, we measure the ACFM (at actual pressure, temp, RH %) and would like to convert this to SCFM (CFMs at standard pressure, temp, RH %). To help everybody, we created these 2 tools that will help with the conversion (don’t worry about a lot of inputs, we will guide you every step of the way):

  • ACFM To SCFM Calculator. This calculator will convert ACFM to SCFM, based on the set of conditions we measure the ACFM at, and equalized to the standard set of conditions (in the US, we usually use 14.7 PSI “sea-level” pressure, 520°R (equal to 60.33°F or 15.74°C), and 0% relative humidity).
  • ACFM To SCFM Formula. We will look at the whole formula (a bit complex; SCFM = ACFM × (Pact – Psat × Φ) / Pstd × Tstd/Tact), and show how it can be simplified substantially if we presume 0% relative humidity (this takes the saturation pressure out of the equation as well).

Quick Example: Let’s say we measured airflow of 100 ACFM at 13.1 PSI actual pressure, 80°F actual temperature, and 60% actual relative humidity. How many SCFM is equal to these 100 ACFM of airflow at standard conditions (14.7 PSI, 520°R (60.33°F), 0% relative humidity)? We use the calculator below, and we can see that 100 ACFM, at these conditions, is equal to 119.24 SCFM at the set standard conditions.

Let’s start with the calculator (followed by an example of how to use the calculator because we have quite a few inputs), and then look at the ACFM to SCFM formula:

 

To illustrate how this calculator works, let’s do 1 example:

Say we want to convert 500 ACFM to SCFM. We measured 500 ACFM at 12.8 PSI pressure, 95°F temp, and 80% relative humidity. We want the SCFM result at US standard conditions (14.7 PSI pressure, 520°R (60.33°F) temp, 0% relative humidity).

Insert ‘500’ ACFM is the 1st field, ‘12.8’ PSI in the 2nd field, ’95’°F in the 3rd field. For saturated pressure at 95°F we use this sat pressure calculator; we see that we have 0.81 PSI sat. pressure, and insert ‘0.81’ PSI in the 4th field. For standard conditions, we insert ‘14.7’ PSI pressure, ‘60.33’°F temperature, and we get this result (screenshot):

online acfm to scfm calculator

You can see that, at these actual and standard conditions, 500 ACFM is equal to 645.17 SCFM. By the way, if you need to do this conversion in reverse – SCFM to ACFM – you can check a similar SCFM to ACFM calculator + formula here.

Alright, let’s have a look at a formula under the hood of this calculator, and how we can simplify these inputs a bit:

ACFM To SCFM Formula

Here is a formula that converts CFMs at actual conditions (ACFM) to CFMs at standard conditions:

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

Here’s what these abbreviations in the ACFM to SCFM 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 a certain temperature.
  • Φ is the actual relative humidity. Example: At 80% relative humidity, we insert 0.8 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 measure actual conditions (Pact, Tact, Φ). The real question is what are the standard conditions at which we determine the SCFM. Here are some of the different standard conditions we use around the world:

  • In the US, we usually use 14.7 PSI pressure (sea-level pressure), 520°R (60.33°F) temperature, and 0% relative humidity.
  • In Europe (UK, Germany, France, etc.) and internationally, we usually use 14.7 PSI pressure, 0°C (32°F), and 0% relative humidity, according to Wikipedia.

These standard conditions are pretty tricky to find (standard temperatures vary quite a lot, from 68°F, 60.33°F, 0°C, 15°C, 20°C to 25°C).

Since the ACFM to SCFM equation looks quite complex, we can simplify it a bit. Namely, if we set the actual relative humidity to 0%, we don’t have to worry about saturated pressure (since the Psat × Φ factor in the equation is always 0, if rel. humidity (Φ) is 0%).

Here is the simplified equation we frequently use in practice:

SCFM = ACFM × Pact / Pstd × Tstd/Tact

From this, we see that the ACFM to SCFM relationship depends on the ratio of actual vs standard pressure (Pact / Pstd) and the ratio of standard vs actual temperature (Tstd/Tact).

Let’s solve another example to illustrate how to use this actual CFM to standard CFM formula:

Say we want to convert 200 ACFM to SCFM. The actual conditions include 12.5 PSI pressure, 100°F (559.67°R), and 0% relative humidity (so we can omit a part of the equation). Our standard conditions are 14.7 PSI, 60.33°F (520°R), and 0% relative humidity. Let’s insert these pressures and temperatures into the equation like this (with the result):

SCFM = 200 ACFM × 12.5 PSI / 14.7 PSI × 520°R/559.69°R = 253.14 SCFM

We see that 200 ACFM, at these actual/standard conditions, is equal to 253.14 SCFM.

You might notice that we have to use temperature in degrees Rankine (°R). A bit of help; you can convert Fahrenheit to Rankine (°F to °R) here, and Rankine to Fahrenheit (°R to °F) here.

We hope that, with the calculator, formula, and this explanation, you are now well equipped to convert ACFM to SCFM yourself. If you need our help, you can use the comment section below, give us a few numbers, and we can do the math together.

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