Fume Hood Face Velocity Calculator
Exhaust CFM from sash opening and face velocity.
Enter your values
Enter the sash width in in.
Enter the sash open height in in.
Enter the target face velocity in FPM.
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.
- Exhaust airflow
- 600 CFM
- Sash opening
- 6 sq ft
- At full 28 in sash
- 933 CFM
- Duct size at 1500 FPM
- 8.6 in dia
Quick answer
Fume hood exhaust equals the sash opening area multiplied by the target face velocity, typically 100 FPM.
CFM = sash width x sash height / 144 x FPM
At a glance
| What it does | Exhaust CFM from sash opening and face velocity. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Sash width, Sash open height, Target face velocity |
| Main output | Exhaust airflow |
| Formula | CFM = sash width x sash height / 144 x FPM |
| Cost | Free — no sign-up, no download |
How to use the Fume Hood Face Velocity Calculator
- 1Measure the sash width and the working open height.
- 2Use 100 FPM unless your safety officer specifies otherwise.
- 3Verify with a velometer at nine points across the opening.
Inputs explained
- Sash width(in)
- Enter the sash width in in.
- Sash open height(in)
- Enter the sash open height in in.
- Target face velocity(FPM)
- Enter the target face velocity in FPM.
Worked example
Using the values the calculator loads with:
Inputs
- Sash width48 in
- Sash open height18 in
- Target face velocity100 FPM
Results
- Exhaust airflow600 CFM
- Sash opening6 sq ft
- At full 28 in sash933 CFM
- Duct size at 1500 FPM8.6 in dia
Frequently asked questions
Is faster always safer?
No — above about 125 FPM turbulence can actually pull contaminants out of the hood.
Variable air volume?
VAV hoods hold face velocity constant as the sash moves, saving a lot of conditioned air.
What do I need to enter into the Fume Hood Face Velocity Calculator?
Just 3 values: sash width, sash open height, target face velocity. 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 Fume Hood Face Velocity Calculator work out the answer?
Fume hood exhaust equals the sash opening area multiplied by the target face velocity, typically 100 FPM. It applies the formula CFM = sash width x sash height / 144 x FPM and shows the working so you can check each step by hand.
Is the Fume Hood Face 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.