Ventilation per Number of People Calculator
Estimate the required ventilation airflow from the number of people in a room and their activity level. Enter the occupant count, pick an activity level, and get the airflow in m³/h.
Occupant-Based Ventilation Requirement
Ventilation per Number of People Formula
Where:
- \(Q\) — required airflow (m³/h)
- \(P\) — number of people in the room
- \(R\) — recommended airflow per person (m³/h), depending on activity level
The formula multiplies the number of occupants by the air supply rate recommended for their level of activity. The result is the total fresh airflow the ventilation system must deliver to the room.
Ventilation per Number of People – Calculation Example
Example: a small office room is occupied by 5 people doing light, quiet work such as reading or working at a desk.
\[ Q = 5 \times 20 = 100 \]
Result: the required ventilation performance is 100 m³/h.
How to Use the Calculator
- Enter The number of people in the room — the maximum number of occupants expected at the same time.
- Select the Activity level that best matches what the occupants are doing: Quiet condition (20 m³/h per person), Moderate activity (40 m³/h per person), or Physical activities (60 m³/h per person).
- Read the Required performance — the total airflow in m³/h that the ventilation system should supply to the room.
What Is Ventilation per Number of People?
Ventilation standards in most countries define the minimum fresh air supply for occupied spaces in one of two ways: per unit of floor area, or per person. The per-person approach is usually the decisive criterion in rooms where occupancy is high relative to floor area — classrooms, meeting rooms, auditoriums, open-plan offices, gyms, and waiting areas.
The reason is physiological: every occupant continuously consumes oxygen, releases carbon dioxide, water vapor, and body heat, and contributes odor. The more people in a room and the more physically active they are, the faster the air quality degrades. Typical design values range from about 20 m³/h per person for sedentary activities up to 60 m³/h or more for physical work or exercise, where both CO₂ production and heat generation rise sharply.
The result \(Q\) represents the volume of fresh air, in cubic meters per hour, that the supply ventilation must deliver so that CO₂ concentration and humidity stay within comfortable, healthy limits. If the calculated airflow is higher than the value obtained from an area-based calculation, the per-person figure usually governs the design — many codes require you to use the larger of the two.
Assumptions, Limitations and Practical Tips
- The calculator uses three simplified activity categories (20, 40, and 60 m³/h per person). National standards and guidelines such as ASHRAE 62.1 or EN 16798-1 give more granular rates; consult them for formal design work.
- The result assumes a steady occupancy count. For rooms with fluctuating occupancy (cinemas, classrooms, open-plan offices), design for the expected peak occupancy, or consider demand-controlled ventilation driven by CO₂ sensors.
- This calculation only accounts for people. In rooms with additional pollutant sources — kitchens, laboratories, smoking areas, industrial processes — source-based airflow requirements may dominate, and the per-person figure alone will not be sufficient.
- Exhaust airflow should roughly balance the supply. Local regulations may require slight overpressure or underpressure (e.g., toilets and kitchens under negative pressure), which affects fan sizing.
- Once you know the required airflow, you can size the system further: estimate the ventilation power, check the overall ventilation airflow requirement, determine the number of diffusers or grilles needed, and calculate the cross-sectional area of rectangular ducts.
Frequently Asked Questions
How do I calculate ventilation per person by hand?
Multiply the number of people by the airflow rate for their activity: quiet seated work needs about 20 m³/h per person, moderate activity about 40 m³/h, and physical work or exercise about 60 m³/h. For example, 12 people in a meeting room doing light office work need \( 12 \times 20 = 240 \) m³/h of fresh air. Add up all occupants present at the same time, including visitors and staff.
How do I convert m³/h to CFM or liters per second?
Divide m³/h by 3.6 to get liters per second, or divide by 1.699 to get cubic feet per minute (CFM). For example, 100 m³/h is about 27.8 l/s or roughly 59 CFM. Conversely, multiply CFM by 1.699 to get m³/h. This conversion is essential when comparing results with fan specifications quoted in imperial units.
What ventilation rate per person is considered healthy?
Common guidance ranges from roughly 20 m³/h per person for sedentary occupancy up to 60 m³/h or more for exercise. As a CO₂ benchmark, indoor concentrations below about 800–1000 ppm generally indicate adequate fresh air, while levels above 1000–1500 ppm often cause drowsiness and complaints. Health-based requirements vary by country and building type, so check your local building code for legally binding values.
What happens if the room is empty or has only occasional visitors?
With zero occupants the per-person requirement is zero, but ventilation may still be needed to control moisture, odors, or off-gassing from materials and furniture. For intermittently used rooms, design for the expected peak occupancy rather than the average, or use demand-controlled ventilation with CO₂ sensors so airflow follows actual occupancy and saves energy during empty periods.
Should I use the per-person or the per-area ventilation rate?
Calculate both and use the larger value, as many standards require. The per-person method usually governs densely occupied rooms like classrooms, gyms, and meeting rooms, while the per-area (per floor square meter) method often governs sparsely occupied spaces like storage areas or large halls with few people. Taking the maximum of the two ensures neither occupancy nor building-related pollutants are neglected.
What are common mistakes when sizing ventilation by occupant count?
Frequent errors include using average instead of peak occupancy, forgetting that exercise rooms need roughly triple the rate of offices, ignoring extra pollutant sources such as kitchens or labs, and confusing supply airflow with fan capacity without accounting for duct losses. Also remember that smoking areas, medical rooms, and industrial spaces have source-based requirements that this per-person calculation alone does not cover.
Is this calculator enough for a code-compliant ventilation design?
It gives a quick, simplified estimate using three activity categories. Formal design should follow detailed standards like ASHRAE 62.1 or EN 16798-1, which define rates per person and per area for specific space types, plus requirements for exhaust, pressure balance, and air distribution. For permit-level work, have a qualified HVAC engineer verify the design against your local building regulations.