Indoor CO₂ Calculator

Model indoor CO₂ buildup from occupancy and ventilation. Find steady-state levels and time to reach 1,000 ppm.

Room Volume (ft³)

Number of Occupants

Ventilation Rate (CFM)

Activity Level

Tab to move between fields

Steady-State CO₂ (ppm)

985

Time to 1,000 ppm (min)0

Required Vent. for 1,000 ppm (CFM)48.7

Per-Person Ventilation (CFM)12.5

Total CO₂ Generation (mL/hr)48,000

How to Use This Calculator

Enter Room Volume (ft³), Number of Occupants, and Ventilation Rate (CFM).
Set Activity Level.
Review the Steady-State CO₂ (ppm) result.
Use Time to 1,000 ppm (min) and Required Vent. for 1,000 ppm (CFM) to inform your decision.

How the result changes with Ventilation Rate (CFM)

Room Volume (ft³): Total room volume (length × width × ceiling height). Typical office ~1,500 ft³.
Number of Occupants: Total people in the room.
Ventilation Rate (CFM): Outdoor air supply rate in cubic feet per minute.
Activity Level: 1 = Sedentary (office), 2 = Light activity (retail), 3 = Moderate (gym/classroom).

Steady-State CO₂ (ppm): Equilibrium CO₂ concentration if occupancy and ventilation remain constant.
Time to 1,000 ppm (min): Minutes from outdoor-air baseline to reach ASHRAE's 1,000 ppm guideline. 0 if steady state is below threshold.
Required Vent. for 1,000 ppm (CFM): Ventilation rate needed to keep steady-state CO₂ at or below 1,000 ppm.
Per-Person Ventilation (CFM): Current ventilation per occupant. ASHRAE 62.1 recommends ≥15 CFM/person.
Total CO₂ Generation (mL/hr): Combined CO₂ output from all occupants at the selected activity level.

Identify Input Parameters
4 parameters
Room Volume (ft³) = 1500, Number of Occupants = 4, Ventilation Rate (CFM) = 50, Activity Level = 1 = 4 input(s) provided
Calculate Steady-State CO₂
Steady-State CO₂ = OUTDOOR_CO2_PPM + (totalGeneration * 1e6) / ventM3Hr
985 = 985
Calculate Time to 1,000 ppm
0 = 0
Calculate Required Vent. for 1,000 ppm
Required Vent. for 1,000 ppm = requiredVentM3Hr / CFM_TO_M3HR
48.7 = 48.7