HVAC · Problem-solving calculator
Outdoor Air Requirement Calculator
Estimate outdoor ventilation airflow from user-defined per-person and per-area ventilation rates.
- Free to use
- Runs in your browser
- Level B · Industry formula
- Last reviewed 2026-08-17
Calculator guide
What this calculator helps you solve
Estimate outdoor ventilation airflow from user-defined per-person and per-area ventilation rates.
Inputs explained
- Design occupants — enter the value that applies to your operation or scenario.
- Outdoor air rate (CFM/person) — enter the value that applies to your operation or scenario.
- Floor area (ft²) — enter the value that applies to your operation or scenario.
- Outdoor air rate (CFM/ft²) — enter the value that applies to your operation or scenario.
Formula and methodology
Worked example
80 occupants at 5 CFM/person plus 5,000 ft² at 0.06 CFM/ft² gives 700 CFM of outdoor air.
How to interpret the result
Enter the ventilation rates required by the applicable design method, code, standard, process, or owner criteria. This calculator combines those rates; it does not select them.
What to keep in mind
- Ventilation requirements vary by occupancy type, jurisdiction, standard edition, and system design.
- System ventilation efficiency and zone calculations can require additional steps beyond this simple summation.
Review approach
This calculator uses deterministic arithmetic and performs the calculation locally in your browser. It is designed to combine operational inputs into a decision-oriented result rather than return a one-line conversion.
Review standard: Level B · Industry formula. How calculator reviews work.
Frequently asked questions
What decision can this calculator support?
Enter the ventilation rates required by the applicable design method, code, standard, process, or owner criteria. This calculator combines those rates; it does not select them.
How is the result calculated?
Outdoor Air CFM = Occupants × CFM/person + Floor Area × CFM/ft².
Are the assumptions universal?
No. Operational, regulatory, technical, and industry assumptions vary. Use values that apply to your situation and verify professional or regulatory requirements where relevant.
Does CalculateMeasure store the values I enter?
The calculation runs in your browser and does not require sending the entered calculator values to a server to produce the result.