Room Volume Calculator
Calculate room air volume in cubic feet & meters. Includes HVAC ventilation airflow sizing (CFM) based on required Air Changes per Hour (ACH).
The floor square footage of the room.
The total 3D cubic air space enclosed within the room walls and ceiling.
CFM (cubic feet per minute) indicates the ventilation fan or HEPA air purifier rating required to cycle the entire room air volume at the specified ACH rate.
Calculates room air volume: Length × Width × Ceiling Height. Also computes ventilation airflow (CFM = Room Volume in ft³ × ACH ÷ 60). A 15×12 ft bedroom with 9 ft ceilings has 1,620 cubic feet of air space and requires a 108 CFM air purifier for 4 air changes per hour.
Room Volume Calculator Formula & Sizing Rules
| Variable | Definition | Standard Units |
|---|---|---|
| V | Air volume enclosed within the room | ft³ or m³ |
| CFM | Airflow in Cubic Feet per Minute: (V × ACH) / 60 | CFM |
Sizing Air Purifiers and Exhaust Fans by Room Volume
Air purifiers and HVAC ventilation fans are rated in CFM (cubic feet of air moved per minute). To size equipment properly, multiply your room volume in cubic feet by your target Air Changes per Hour (ACH, typically 4 to 5 for clean air), then divide by 60 minutes.
Common Project Sizing Mistakes
- Sizing air purifiers by square feet alone without accounting for high 10–12 ft ceilings
- Assuming all rooms require the same air change rate (kitchens and workshops require higher ACH)
Frequently Asked Questions
How do you calculate the volume of a room?▼
How do you calculate CFM needed for a room?▼
How do you calculate room volume in cubic meters?▼
How does ceiling height impact heating and air conditioning requirements?▼
Authoritative Sources & Reference Standards
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811 — National Institute of Standards and Technology (NIST). Verified 2026-10-01.
Official SI unit definitions, conversion factors (Appendix B), and precision standards for cubic meters, liters, and US customary units.
- ASHRAE Standard 62.1 & 62.2: Ventilation and Acceptable Indoor Air Quality — American Society of Heating, Refrigerating and Air-Conditioning Engineers. Verified 2026-10-01.
Standard air changes per hour (ACH) and ventilation rates per room cubic volume.