Enter the airflow in CFM and select the round duct size to determine the air velocity in meters per second, or use the formula and conversion table below to verify the result manually.
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CFM to m/s Formula
The following formula is used to convert airflow in cubic feet per minute into air velocity in meters per second for a duct of known cross-sectional area.
v = (CFM × 0.000471947) / A
Variables:
- v is the air velocity in meters per second (m/s)
- CFM is the airflow in cubic feet per minute
- 0.000471947 converts CFM to cubic meters per second
- A is the duct cross-sectional area in square meters
To calculate air velocity, first convert the airflow from CFM to m³/s, then divide by the duct area in m².
What is CFM to m/s Conversion?
CFM is a volumetric flow rate, while m/s is a linear air velocity. That means you cannot convert directly from CFM to m/s unless you also know the duct size or cross-sectional area. A larger duct spreads the same airflow across more area, which lowers velocity, while a smaller duct increases the air speed for the same CFM.
This conversion is commonly used in HVAC, ventilation, dust collection, and airflow analysis when comparing fan ratings to duct performance. Once the duct area is known, the conversion becomes straightforward using the relationship between flow, velocity, and area.
How to Calculate CFM to m/s?
The following steps outline how to calculate air velocity from airflow in CFM.
- First, determine the airflow rate in cubic feet per minute (CFM).
- Next, determine the round duct diameter or the duct cross-sectional area in square meters.
- Convert the CFM value to cubic meters per second using 1 CFM = 0.000471947 m³/s.
- Finally, divide the airflow in m³/s by the duct area to calculate the velocity in m/s.
- After inserting the values and calculating the result, check your answer with the calculator above.
Common Round Duct Areas
- 4 in round duct: A ≈ 0.00811 m²
- 6 in round duct: A ≈ 0.01824 m²
- 8 in round duct: A ≈ 0.03243 m²
- 10 in round duct: A ≈ 0.05067 m²
- 12 in round duct: A ≈ 0.07297 m²
- 14 in round duct: A ≈ 0.09931 m²
CFM to m/s Conversion Table
The table below shows the approximate air velocity for a 200 CFM airflow in several common round duct sizes.
| Duct Size | Approx. Area (m²) | Velocity at 200 CFM (m/s) |
|---|---|---|
| Round duct – 4 in | 0.00811 | ≈ 11.64 m/s |
| Round duct – 6 in | 0.01824 | ≈ 5.17 m/s |
| Round duct – 8 in | 0.03243 | ≈ 2.91 m/s |
| Round duct – 10 in | 0.05067 | ≈ 1.86 m/s |
| Round duct – 12 in | 0.07297 | ≈ 1.29 m/s |
| Round duct – 14 in | 0.09931 | ≈ 0.95 m/s |
Example Problem
Use the following variables as an example problem to test your knowledge.
Airflow (CFM) = 200
Duct Size = 8 in round duct
Duct Area (A) = 0.03243 m²
Velocity (v) = (200 × 0.000471947) / 0.03243 = 2.91 m/s