Office Ventilation CFM Calculator
Total and outdoor airflow for an office.
Enter your values
Enter the floor area in sq ft.
Enter the occupants you are working with.
Enter the supply rate in CFM/sq ft.
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.
- 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
At a glance
| What it does | Total and outdoor airflow for an office. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Floor area, Occupants, Supply rate |
| Main output | Total supply air |
| Formula | OA = 5 x people + 0.06 x area |
| Cost | Free — no sign-up, no download |
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.
Inputs explained
- Floor area(sq ft)
- Enter the floor area in sq ft.
- Occupants
- Enter the occupants you are working with.
- Supply rate(CFM/sq ft)
- Enter the supply rate in CFM/sq ft.
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.
What do I need to enter into the Office Ventilation CFM Calculator?
Just 3 values: floor area, occupants, supply rate. 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 Office Ventilation CFM Calculator work out the 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. It applies the formula OA = 5 x people + 0.06 x area and shows the working so you can check each step by hand.
Is the Office Ventilation CFM 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.