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Easily calculate air velocity with our free Air Velocity Calculator. Learn formulas, methods, and FAQs for accurate air speed measurement at any altitude.
Air velocity is one of the most important values in fluid mechanics, HVAC systems, and aviation. It tells us how fast air is moving through a duct, pipe, or even at different altitudes in the atmosphere. To make this process simple, we developed our Air Velocity Calculator, which allows anyone to calculate air speed quickly without struggling with complex equations.
This tool is designed for students, engineers, pilots, and HVAC technicians who need quick and reliable results. You just enter your known values, and the calculator does the math for you in seconds.
Air velocity can be calculated in two main ways:
Method 1: Using Volumetric Flow Rate
The formula is:
V = Q / A
Where:
For a circular duct:
A = π × r²
For a rectangular duct:
A = l × w
This method is most common in HVAC systems, where airflow in cubic feet per minute (CFM) is measured and then divided by the duct area to find the velocity.
Method 2: Using Differential Pressure
Another way to calculate air velocity is by using a Pitot tube and manometer to measure velocity pressure.
For standard air conditions:
V = 4005 × √ΔP
Where:
If air conditions are not standard, we correct for density using:
V = 1096.7 × √(hv / d)
Where:
Barometric pressure decreases with altitude. To correct barometric pressure, a standard lapse rate is used. On average, pressure drops about 1 inch of mercury for every 1000 feet of elevation gain.
Corrected Pressure Formula:
P = P₀ − (h × 0.034)
Where:
For every 1000 feet increase in altitude, barometric pressure decreases by roughly 1 inch of mercury (inHg) or about 34 millibars. This is an approximation because the actual rate can change depending on weather and temperature.
At 30,000 feet, air density is much lower than at sea level. Since velocity depends on pressure and density, the same velocity pressure reading will give a higher air velocity at 30,000 feet compared to sea level.
For example:
V = 1096.7 × √(hv / d)
If hv = 1 in. w.c. and d = 0.018 lb/ft³ (air density at 30,000 ft), the velocity will be much greater than the same pressure measured at sea level (d ≈ 0.076 lb/ft³).
This shows why airplanes fly faster at high altitudes even with relatively small pressure differences.
Our calculator also shows step-by-step calculations so you can understand how the result was obtained.
Air velocity is a key measurement in HVAC design, fluid mechanics, and aviation. Whether you are checking duct airflow or calculating true airspeed at 30,000 feet, our Air Velocity Calculator makes the process simple and accurate. Instead of memorizing formulas, you just enter values, and the tool does all the work.
If you want reliable results and easy learning, this calculator is your go-to solution.
It is an online tool that calculates air speed based on either flow rate and duct area or velocity pressure and air density.
Yes, you can view results in feet per minute, feet per second, meters per second, miles per hour, and kilometers per hour.
You can adjust barometric pressure using the standard lapse rate, about 1 inHg per 1000 feet, and then apply the air velocity formula with corrected density.
Absolutely. HVAC engineers can quickly calculate duct velocities and airflow distribution without manual formulas.
Yes, it helps estimate true airspeed using pressure and density corrections at higher altitudes.