Office Ventilation CFM Calculator
Total and outdoor airflow for an office.
Enter your values
ⓘ Live results
Results
- Total supply air
- 2,500 CFM
- Outdoor air
- 240 CFM
- Outdoor air fraction
- 9.6%
- Per person total
- 138.9 CFM
- Cooling capacity implied
- 6.3 tons
Quick answer
Offices typically need 1 CFM per square foot of supply air with 5 CFM per person plus 0.06 per sq ft of outdoor air.
OA = 5 x people + 0.06 x area
How to use the Office Ventilation CFM Calculator
- 1Enter the floor area and realistic design occupancy.
- 2Set the supply rate — 1 CFM per sq ft suits most offices.
- 3Confirm the outdoor air damper can actually deliver the OA figure.
Worked example
Using the values the calculator loads with:
Inputs
- Floor area2500 sq ft
- Occupants18
- Supply rate1 CFM/sq ft
Results
- Total supply air2,500 CFM
- Outdoor air240 CFM
- Outdoor air fraction9.6%
- Per person total138.9 CFM
- Cooling capacity implied6.3 tons
Frequently asked questions
Why is my office stuffy?
Usually the outdoor air damper is closed or the economiser has failed; check CO2 levels.
Dense meeting rooms?
Size those separately — they can need 3-4 times the area-based rate.
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.