Room CO₂ Level Calculator (Ventilation)
How high carbon dioxide builds up in a room with a given number of people and amount of fresh air, and how much ventilation keeps it at 1000 ppm.
Results
The dashed line marks the value you entered.
What this tool does
CO₂ is a good tracer for stale air: people breathe it out at a steady rate and fresh air dilutes it, so the level climbs towards a balance and stays there. Two people sleeping in a small closed bedroom can easily pass 2000 ppm by morning, while about 1000 ppm is a widely used benchmark for adequate ventilation. A resting adult gives off roughly 0.005 litres of CO₂ per second — less when asleep, several times more when exercising. The model assumes the air is well mixed and starts from outdoor levels.
Formula
C(t) = C_ss + (C₀ − C_ss) e^(−Q t ÷ V) · C_ss = C_out + G ÷ Q
Variables
| Symbol | Meaning | Unit |
|---|---|---|
vr | Room volume | m³ |
np | People in the room | — |
gp | CO₂ breathed out per person | L/s |
q | Fresh air coming in | m³/h |
co | Outdoor CO₂ | ppm |
t | Time since the room was aired | h |
C | CO₂ after that time | ppm |
SS | Level it settles at | ppm |
QN | Fresh air needed to stay at 1000 ppm | m³/h |
AC | Air changes per hour now | /h |
Worked example
- Room volume30 m³
- People in the room2
- CO₂ breathed out per person0.005 L/s
- Fresh air coming in15 m³/h
- Outdoor CO₂420 ppm
- Time since the room was aired8 h
- CO₂ after that time2776 ppm
- Level it settles at2820 ppm
- Fresh air needed to stay at 1000 ppm62.1 m³/h
- Air changes per hour now0.50 /h
Limitations
- The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.