CO2 Ventilation Rate Calculator
Outdoor air needed to hold a CO2 target.
Enter your values
Enter the indoor co2 target in ppm.
Enter the outdoor co2 in ppm.
Enter the occupants you are working with.
Choose one of: Seated at rest, Light office work, Moderate activity, Exercise.
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.
- Per person airflow
- 18.3 CFM
- Total outdoor air
- 457 CFM
- In L/s per person
- 8.6
- Steady CO2 at 15 CFM/person
- 1,127 ppm
Quick answer
Steady-state CO2 depends on the outdoor air per person; about 15 CFM per person holds roughly 1,000 ppm.
CFM per person = CO2 generation / (Ctarget - Coutdoor)
At a glance
| What it does | Outdoor air needed to hold a CO2 target. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Indoor CO2 target, Outdoor CO2, Occupants, Activity |
| Main output | Per person airflow |
| Formula | CFM per person = CO2 generation / (Ctarget - Coutdoor) |
| Cost | Free — no sign-up, no download |
How to use the CO2 Ventilation Rate Calculator
- 1Set the CO2 target — 800 ppm for high cognitive performance, 1,000 ppm for general comfort.
- 2Enter outdoor CO2, typically 420 ppm today.
- 3Multiply by occupants and compare against your current outdoor air damper setting.
Inputs explained
- Indoor CO2 target(ppm)
- Enter the indoor co2 target in ppm.
- Outdoor CO2(ppm)
- Enter the outdoor co2 in ppm.
- Occupants
- Enter the occupants you are working with.
- Activity
- Choose one of: Seated at rest, Light office work, Moderate activity, Exercise.
Worked example
Using the values the calculator loads with:
Inputs
- Indoor CO2 target1000 ppm
- Outdoor CO2420 ppm
- Occupants25
- ActivityLight office work
Results
- Per person airflow18.3 CFM
- Total outdoor air457 CFM
- In L/s per person8.6
- Steady CO2 at 15 CFM/person1,127 ppm
Frequently asked questions
Is CO2 itself harmful at 1,000 ppm?
Not directly, but it tracks other bio-effluents and studies link 1,000+ ppm to reduced decision-making scores.
How long to reach steady state?
Roughly three air changes, so 30-90 minutes in most rooms.
What do I need to enter into the CO2 Ventilation Rate Calculator?
Just 4 values: indoor co2 target, outdoor co2, occupants, activity. 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 CO2 Ventilation Rate Calculator work out the answer?
Steady-state CO2 depends on the outdoor air per person; about 15 CFM per person holds roughly 1,000 ppm. It applies the formula CFM per person = CO2 generation / (Ctarget - Coutdoor) and shows the working so you can check each step by hand.
Is the CO2 Ventilation Rate 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.