CFM per Room Calculator
Calculate the required CFM (Cubic Feet per Minute) of airflow needed for a room based on its length, width, ceiling height, and desired air changes per hour (ACH).
Typical: Bedroom 4–6, Living Room 4–6, Kitchen 7–8, Bathroom 6–8, Office 4–6
Formula
Step 1 — Room Volume (ft³):
Volume = Length × Width × Ceiling Height
Step 2 — Required CFM:
CFM = (Volume × ACH) / 60
Where ACH is Air Changes per Hour — the number of times the entire air volume of the room is replaced in one hour. Dividing by 60 converts from cubic feet per hour to cubic feet per minute.
Example: A 15 ft × 12 ft room with an 8 ft ceiling and 6 ACH:
Volume = 15 × 12 × 8 = 1,440 ft³
CFM = (1,440 × 6) / 60 = 144 CFM
Assumptions & References
- All room dimensions are entered in feet; the result is in CFM (Cubic Feet per Minute).
- The formula assumes uniform air distribution throughout the room volume.
- Recommended ACH values vary by room type (ASHRAE Standard 62.1):
- Bedrooms / Living Rooms: 4–6 ACH
- Kitchens: 7–8 ACH
- Bathrooms: 6–8 ACH
- Home Offices: 4–6 ACH
- Commercial spaces: 6–10+ ACH (consult ASHRAE 62.1)
- This calculator provides a baseline estimate. Actual HVAC design should account for heat loads, humidity, occupancy, and local building codes.
- References: ASHRAE Standard 62.1 (Ventilation for Acceptable Indoor Air Quality); ACCA Manual D (Residential Duct Systems).