Wind Speed to CFM Calculator
Calculate airflow in cubic feet per minute (CFM) from wind speed and opening area. Enter wind speed and the area through which air flows to estimate the corresponding volumetric airflow.
Airflow Results
How do you calculate CFM from wind speed?
CFM means cubic feet per minute. To calculate airflow from air velocity, you need both the air speed and the cross-sectional area through which the air moves.
$$Q = V \times A$$
$$CFM = Velocity_{ft/min} \times Area_{ft^2}$$
Wind speed must therefore be converted to feet per minute before multiplying it by an area measured in square feet.
What is the wind speed to CFM formula?
When wind speed is expressed in miles per hour:
$$CFM = Wind\ Speed_{mph} \times 88 \times Area_{ft^2}$$
The value 88 comes from the conversion:
$$1\ mph = 88\ ft/min$$
Therefore:
$$CFM = mph \times 88 \times Area$$
Example: 20 mph wind through a 10 ft² opening
Convert 20 mph to feet per minute:
$$20 \times 88 = 1760\ ft/min$$
$$CFM = 1760 \times 10 = 17,600\ CFM$$
With a coefficient of 1.00, the theoretical airflow would therefore be approximately 17,600 CFM.
Can you calculate CFM from wind speed alone?
No. Wind speed tells you how fast air is moving, but CFM measures how much air passes through an area per unit of time.
$$CFM = Velocity \times Area$$
Without knowing the area, there is no unique CFM value for a given wind speed.
Why does opening area affect CFM?
At the same velocity, a larger opening allows more air volume to pass through every minute.
$$Area \uparrow \Rightarrow CFM \uparrow$$
For example, doubling the opening area while maintaining the same average velocity approximately doubles the theoretical airflow.
How do you convert mph to CFM?
First convert the wind speed from miles per hour to feet per minute:
$$Velocity_{ft/min} = mph \times 88$$
Then multiply by the opening area in square feet:
$$CFM = mph \times 88 \times Area_{ft^2}$$
How do you convert m/s to CFM?
One meter per second equals approximately 196.85 feet per minute:
$$1\ m/s \approx 196.85\ ft/min$$
$$CFM = Velocity_{m/s} \times 196.85 \times Area_{ft^2}$$
How do you calculate CFM from wind speed and square feet?
When wind speed is in mph and area is in square feet, use:
$$CFM = Wind\ Speed \times 88 \times Area$$
Wind Speed to CFM Chart
The table below assumes a 10 ft² opening and a flow coefficient of 1.00. It demonstrates why the opening area must always be specified when converting wind speed to CFM.
| Wind Speed | Velocity | CFM Through 10 ft² |
|---|---|---|
| 5 mph | 440 ft/min | 4,400 CFM |
| 10 mph | 880 ft/min | 8,800 CFM |
| 15 mph | 1,320 ft/min | 13,200 CFM |
| 20 mph | 1,760 ft/min | 17,600 CFM |
| 25 mph | 2,200 ft/min | 22,000 CFM |
| 30 mph | 2,640 ft/min | 26,400 CFM |
| 40 mph | 3,520 ft/min | 35,200 CFM |
| 50 mph | 4,400 ft/min | 44,000 CFM |
| 60 mph | 5,280 ft/min | 52,800 CFM |
How do you calculate CFM for a round opening?
First calculate the cross-sectional area of the circular opening:
$$A = \pi \left( \frac{D}{2} \right)^2$$
Then multiply the area by airflow velocity:
$$CFM = Velocity_{ft/min} \times \pi \left( \frac{D}{2} \right)^2$$
How do you calculate CFM for a rectangular opening?
For a rectangular opening, multiply its width by its height:
$$Area = Width \times Height$$
$$CFM = Velocity \times Width \times Height$$
What is the difference between CFM and wind speed?
Wind speed is a velocity. It describes how quickly the air moves, such as 20 mph or 10 m/s.
CFM is a volumetric flow rate. It describes how much air passes a particular point each minute.
$$Wind\ Speed = Distance / Time$$
$$CFM = Volume / Time$$
Why is the calculated CFM sometimes higher than expected?
A simple velocity-times-area calculation assumes the stated velocity exists uniformly across the entire opening. Real airflow can be much more complicated.
Screens, louvers, bends, filters, pressure differences, turbulence, obstructions, and changing wind direction can reduce the actual airflow.
What is an airflow coefficient?
A flow coefficient can be used as a simple correction factor for losses or non-ideal flow.
$$Actual\ CFM = Theoretical\ CFM \times Flow\ Coefficient$$
A value of 1.00 means no reduction. Lower values produce a lower estimated actual airflow.
Is wind speed to CFM the same as HVAC airflow?
The basic mathematical relationship is the same: airflow equals velocity multiplied by area. However, HVAC systems are normally designed around controlled pressure differences, duct geometry, fans, filters, fittings, and measured airflow rather than arbitrary outdoor wind speed.
Can wind speed be converted to CFM through a vent?
Yes, as a preliminary estimate, provided you know the effective opening area and the average air velocity through that opening.
For a real vent, the actual CFM may be lower because the vent creates resistance and the velocity may not be uniform across the opening.
How does doubling wind speed affect CFM?
If the opening area stays constant and the actual air velocity doubles, the theoretical CFM also doubles.
$$Velocity \times 2 \Rightarrow CFM \times 2$$
This is different from wind pressure, which increases approximately with the square of wind speed.
How does doubling the opening area affect CFM?
With the same average velocity, doubling the opening area doubles the theoretical airflow.
$$Area \times 2 \Rightarrow CFM \times 2$$
What is the formula for CFM?
$$\boxed{ CFM = Velocity_{ft/min} \times Area_{ft^2} }$$
This is the core equation used by the calculator.
Wind speed to CFM FAQ
No. Wind speed alone is not enough. You also need the cross-sectional area through which the air flows.
CFM = air velocity in ft/min × opening area in ft². For mph, CFM = mph × 88 × area in ft².
It depends on the opening area. Through a 10 ft² opening, 10 mph corresponds to approximately 8,800 CFM under ideal full-area flow conditions.
Through a 10 ft² opening, 20 mph corresponds to approximately 17,600 CFM under ideal conditions. A different opening area produces a different CFM.
Through a 10 ft² opening, 30 mph corresponds to approximately 26,400 CFM under ideal full-area flow conditions.
Wind speed determines velocity, but airflow also depends on the area through which the air moves. CFM is therefore a combination of velocity and area.
No. CFM is cubic feet per minute, while cubic feet per second measures the same type of quantity over a different time interval. 1 CFS equals 60 CFM.