Enter the flow rate, blower speed, and blower diameter into the calculator to determine the missing variable.

Air Blower Capacity Calculator

Enter any 2 values to solve the third
(based on a simplified fan affinity-law estimate with φ ≈ 0.30, so Q ∝ N·D³).

Disclaimer: Uses a nominal flow coefficient φ ≈ 0.30. Actual blower capacity depends on blower/fan design and operating point (static pressure), and must be confirmed from manufacturer curves or test data.

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Air Blower Capacity Formula

The following relationship is a fan affinity-law estimate that assumes a nominal (dimensionless) flow coefficient of about φ ≈ 0.30. With Q in CFM, N in RPM, and D in inches, this becomes:

Q \approx 1.74 \times 10^{-4} \cdot N \cdot D^3

Variables:

  • Q is the flow rate (CFM)
  • N is the blower speed (RPM)
  • D is the blower/impeller diameter (inches)

What is an Air Blower?

An air blower is a device used to move air at a relatively high flow rate with a low to moderate pressure rise (generally higher pressure than a typical fan, but lower than a compressor). It is commonly used in various industrial and commercial applications, such as ventilation, cooling, and material handling. Air blowers can be powered by electric motors, gasoline engines, or other power sources, and they come in various designs, including centrifugal, axial, and positive displacement blowers. The performance of an air blower is typically characterized by its flow rate, pressure, and efficiency.

How to Calculate Air Blower Capacity?

The following steps outline how to calculate the Air Blower Capacity.

  1. First, determine the blower speed (N) in RPM.
  2. Next, determine the blower diameter (D) in inches.
  3. Finally, estimate the flow rate (Q) using: Q ≈ 1.74 × 10−4 · N · D3 (this corresponds to φ ≈ 0.30 and is an approximation).
  4. If any two of the variables are known, the third can be calculated by rearranging the same equation.
  5. After inserting the values and calculating the result, check your answer with the calculator above.

Example Problem : 

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

Blower speed (N) = 1500 RPM

Blower diameter (D) = 10 inches

Calculate the flow rate (Q).