Cfm Calculator

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Living rooms: 4–6; bathrooms: 6–8; kitchens: 8–15.
Construction

Calculate the required CFM (cubic feet per minute) of ventilation for a room based on volume and air changes per hour.

Formula

CFM = (Room Volume × ACH) ÷ 60
  • ACH = air changes per hour; 60 converts from per-hour to per-minute.
  • Recommended ACH: bedroom 4–6, bathroom 6–8, kitchen 8–15.

20×15×9 ft room, 6 ACH

Inputs
  • Room Length: 20 ft
  • Room Width: 15 ft
  • Ceiling Height: 9 ft
  • Air Changes per Hour (ACH): 6

Volume = 2700 cu ft. CFM = 2700×6/60 = 270 CFM.

Frequently asked questions

How do I measure actual CFM?
Use an anemometer at the supply vent. CFM = velocity (ft/min) × vent area (sq ft).