Convert CFM to lb/min or reverse the calculation using custom gas density, a named dry-air reference near 70°F and 1 atm, or actual temperature and absolute pressure.

Use density at the same conditions as the volume flow. CFM alone does not determine mass flow.

Default: rounded dry-air reference near 70°F and 1 atm. Replace it for other gas conditions.

CFM to lb/min Formula

The following formula is used to convert a volumetric flow rate in CFM to a mass flow rate in lb/min.

lb / min = CFM × ρ

The reverse relationship can also be written as:

CFM = (lb / min) / ρ

Variables:

  • lb/min is the mass flow rate in pounds per minute
  • CFM is the volumetric flow rate in cubic feet per minute
  • ρ is the density of the air or gas in pounds per cubic foot (lb/ft³)

To calculate lb/min, multiply the flow rate in CFM by the assumed density of the fluid in lb/ft³.

What is CFM to lb/min Conversion?

CFM measures the volumetric flow of a fluid, while lb/min measures the mass flow. Because mass depends on density, the conversion from CFM to lb/min requires an assumed density for the air or gas being measured. This is why the same CFM value can produce different lb/min values for cool air, warm air, hot air, or natural gas.

For quick engineering estimates, common density assumptions are often used. A rounded dry-air reference near 70°F and 1 atmosphere is 0.075 lb/ft³; it is not an exact density or a universal SCFM definition. Cooler air is denser and produces a slightly higher lb/min value at the same CFM, while warmer air is less dense and produces a lower lb/min value.

How to Convert CFM to lb/min?

The following steps outline how to convert CFM to lb/min.

  1. First, determine the volumetric flow rate in cubic feet per minute (CFM).
  2. Next, choose the appropriate air or gas condition and identify its density in lb/ft³.
  3. Multiply the CFM value by the density using the formula lb/min = CFM × ρ.
  4. After calculating the result, check your answer with the converter above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Flow Rate (CFM) = 100

Condition = Rounded dry-air reference (near 70°F, 1 atm)

Density (ρ) = 0.075 lb/ft³

lb/min = 100 × 0.075 = 7.5 lb/min

CFM to lb/min Conversion Table

The table below uses illustrative density assumptions for a 100 CFM flow rate. These are not gas-property ratings; volume flow and density must describe the same conditions.

Condition Density (lb/ft³) 100 CFM in lb/min
Rounded dry-air reference (near 70°F, 1 atm) 0.075 7.5
Illustrative cool-air density 0.080 8.0
Illustrative warm-air density 0.071 7.1
Illustrative hot-air density 0.068 6.8
Illustrative natural-gas density 0.044 4.4

These values are approximate and are most useful for quick estimates. If you need higher accuracy, use the actual density of the gas at the specific operating temperature and pressure.