Indoor CO₂ Calculator

Every person exhales CO₂ at a rate that depends on how active they are, and this calculator uses that per-person generation rate to model how a room's CO₂ level rises and levels off. It assigns a fixed generation rate by activity level — 0.012 m³/hr for sedentary occupants (~200 mL/min), 0.021 m³/hr for light activity (~350 mL/min), and 0.030 m³/hr for moderate activity like a gym or classroom (~500 mL/min) — multiplies by your occupant count, and combines that with your ventilation rate to solve the steady-state formula C_ss = C_outdoor + (N × G × 10⁶)/Q, starting from a 420 ppm outdoor baseline. Because real rooms don't jump straight to steady state, it also solves the exponential buildup equation for how long it takes to cross the traditional 1,000 ppm CO₂ guideline threshold long associated with ASHRAE ventilation standards (a widely used proxy for "the room needs more fresh air," since CO₂ itself is only mildly harmful at that level but correlates with reduced ventilation of everything else people exhale).

Two additional outputs turn the model around: the ventilation rate that would be required to hold steady-state CO₂ at exactly 1,000 ppm, and your current ventilation per occupant, benchmarked here against the commonly cited ≥15 CFM/person figure derived from ANSI/ASHRAE Standard 62.1's minimum outdoor-air rates for typical office occupant density. This is a single well-mixed zone model — it assumes occupants and fresh air are evenly distributed rather than the room having stagnant corners or a bunched-up crowd near one wall, and it holds occupancy and activity level constant throughout, so a shifting crowd (people arriving and leaving) or a mid-session activity change will make the actual trajectory diverge from the smooth exponential curve predicted here.