Cleanroom engineering tool

FFU quantity calculator

Estimate the number of fan filter units needed for a cleanroom. Enter the required total airflow and the delivered airflow of one FFU to get a whole-unit count.

Estimate FFU count

Results update as you type.

Enter two airflow values

The total supply airflow needed for the cleanroom or zone.

Use a design or measured airflow value.

The airflow one selected FFU can deliver at its intended operating point.

Check the supplier's data at the installed pressure and speed.

This is a preliminary airflow-based estimate. It does not check ceiling coverage, airflow distribution, or cleanroom classification.

How the estimate works

Divide the required total airflow by the delivered airflow of one FFU, using the same unit for both values. Round the result up because a fraction of an FFU cannot be installed. The calculator converts m³/h and CFM when the inputs use different units.

Raw quantity = required airflow ÷ delivered airflow per FFU
Preliminary FFU count = round up (raw quantity)

For example, 10,000 m³/h divided by 1,200 m³/h per FFU equals 8.33. The preliminary count is therefore 9 FFUs, with a combined nominal airflow of 10,800 m³/h at the entered per-unit operating point.

Before finalizing the FFU layout

This count answers an airflow question only. A final selection also needs to account for the actual FFU performance and how the units fit the cleanroom ceiling and airflow plan.

  • Confirm the delivered airflow per FFU at the expected filter condition, speed, and installed static pressure.
  • Check ceiling grid dimensions, available installation area, coverage, and airflow distribution over critical zones.
  • Review the return-air path, pressure relationships, and project-specific cleanliness requirements with a cleanroom engineer.
Discuss your FFU project

Further reading: Wiskind Cleanroom's FFU coverage and ceiling layout guide.