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HVAC & Airflow

Air Velocity Calculator

Duct air speed in FPM, m/s and mph.

Enter your values

Enter the airflow in CFM.

Enter the duct area in sq ft.

Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.

Results
Velocity
1,091 FPM
In m/s
5.54
In mph
12.4
In km/h
19.95

Quick answer

Air velocity is the volumetric flow rate divided by the cross-sectional area of the duct.

v = Q / A

At a glance

What it doesDuct air speed in FPM, m/s and mph.
CategoryHVAC & Airflow
Inputs neededAirflow, Duct area
Main outputVelocity
Formulav = Q / A
CostFree — no sign-up, no download

How to use the Air Velocity Calculator

  1. 1Enter the airflow in CFM.
  2. 2Enter the duct's free cross-sectional area in square feet.
  3. 3Compare against the target velocity for that duct type.

Inputs explained

Airflow(CFM)
Enter the airflow in CFM.
Duct area(sq ft)
Enter the duct area in sq ft.

Worked example

Using the values the calculator loads with:

Inputs

  • Airflow600 CFM
  • Duct area0.55 sq ft

Results

  • Velocity1,091 FPM
  • In m/s5.54
  • In mph12.4
  • In km/h19.95

Frequently asked questions

What velocity suits a main trunk?

Residential trunks usually run 700–900 FPM; commercial mains often 1200–1800 FPM.

What about return air?

Keep returns slower — around 500–700 FPM — because return grilles transmit noise easily.

What do I need to enter into the Air Velocity Calculator?

Just 2 values: airflow, duct area. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.

How does the Air Velocity Calculator work out the answer?

Air velocity is the volumetric flow rate divided by the cross-sectional area of the duct. It applies the formula v = Q / A and shows the working so you can check each step by hand.

Is the Air Velocity Calculator free, and do I need an account?

It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.

Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.