Fume Hood Face Velocity Calculator

Calculator Inputs

Enter airflow, sash size, target band, and optional velocity readings from traverse or point measurements.

Airflow

Airflow Unit

Velocity Unit for Measured Points

Sash Width

Sash Height

Dimension Unit

Target Minimum Velocity (FPM)

Target Maximum Velocity (FPM)

Point 1

Point 2

Point 3

Point 4

Point 5

Point 6

Point 7

Point 8

Example Data Table

This example shows a typical commissioning or verification scenario for a fume hood opening.

Airflow	Width	Height	Area	Theoretical Velocity	Measured Points	Average Measured	Status
525 CFM	3.5 ft	1.5 ft	5.25 ft²	100.00 FPM	96, 102, 99, 104, 97, 101	99.83 FPM	Within target band
780 CFM	1.1 m	0.45 m	5.33 ft²	146.34 FPM	142, 148, 145, 150, 144, 147	146.00 FPM	Above many common targets

Formula Used

1) Opening Area

Area = Width × Height

2) Theoretical Face Velocity

Face Velocity = Airflow ÷ Opening Area

3) Average Measured Velocity

Average = Sum of Test Point Velocities ÷ Number of Points

4) Uniformity Percentage

Uniformity % = Minimum Reading ÷ Maximum Reading × 100

5) Required Airflow for a Target Velocity

Required Airflow = Opening Area × Target Face Velocity

Unit support is built in. Airflow is normalized to CFM, dimensions to feet, and measured face velocity to FPM for consistent reporting.

How to Use This Calculator

Enter the hood airflow value and choose its unit.
Enter the sash width and sash height, then pick the dimension unit.
Set the target minimum and maximum face velocity band in FPM.
Optionally add up to eight measured velocity readings from field testing.
Click the calculate button to show results above the form.
Review the theoretical velocity, measured average, required airflow, status band, and graph.
Use the CSV or PDF buttons to export the result summary.

FAQs

1) What is fume hood face velocity?

It is the average speed of air moving through the hood opening. It helps show whether containment airflow is strong enough for safe capture and exhaust performance.

2) Why compare theoretical and measured velocity?

Theoretical velocity comes from airflow and opening area. Measured velocity reflects real field conditions. Comparing both highlights losses, uneven flow, leakage, or balancing issues.

3) What target range should I use?

Target ranges vary by facility criteria, hood type, risk level, and governing standards. Many labs use a band near 80 to 120 FPM, but project requirements should control.

4) Why is opening size important?

A larger sash opening spreads the same airflow over more area, which lowers face velocity. A smaller opening raises velocity if airflow stays unchanged.

5) What does uniformity percentage mean?

Uniformity compares the lowest and highest measured points. Higher uniformity suggests more even airflow across the opening, while low uniformity can indicate dead zones or turbulence.

6) Can I use metric inputs?

Yes. The calculator accepts metric dimension options and alternative airflow units. It automatically converts them into consistent internal values for the final report.

7) Why would measured values differ from calculated values?

Real installations include turbulence, room drafts, sash position changes, leakage, obstructions, and calibration differences. These factors often make field readings diverge from ideal calculations.

8) Is this tool enough for formal certification?

It is useful for estimating, checking, and documenting values, but formal certification should follow the required test procedure, instrumentation, and project or regulatory criteria.