Fume Hood Face Velocity Calculator
Exhaust CFM from sash opening and face velocity.
Enter your values
ⓘ Live results
Results
- 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
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.
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.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.