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CFM Calculator

Free online CFM (Cubic Feet per Minute) calculator for HVAC, ventilation, and air flow calculations. Calculate required air flow based on room size, air changes, or cooling/heating load.

The CFM Calculator helps you determine the required air flow rate in Cubic Feet per Minute for HVAC systems, ventilation, and cooling applications. Calculate based on room volume, desired air changes per hour, or heating/cooling load.
Calculation Method
Room Dimensions
Air InCFM = Volume × ACH / 60

What is CFM?

CFM (Cubic Feet per Minute) is a measurement of air flow rate or volume of air moved per minute. It's the standard unit for measuring ventilation, HVAC capacity, and fan performance in the United States. CFM determines how quickly air is exchanged in a room or space. For example, 100 CFM means 100 cubic feet of air is moved every minute. Proper CFM ensures adequate ventilation, temperature control, and air quality. It's calculated based on room volume and desired air changes per hour (ACH), or from heating/cooling load requirements.

CFM Calculation Formulas

1. CFM = (Room Volume in ft³ × ACH) / 60

2. CFM = (BTU/hr) / (1.08 × ΔT)

3. CFM = (BTU/hr) / (1.08 × ΔT)

Where: ACH = Air Changes per Hour, ΔT = Temperature difference (°F)

Recommended Air Changes per Hour

Residential living areas: 4-6 ACH

Bedrooms: 3-4 ACH

Kitchens: 8-12 ACH

Bathrooms: 8-12 ACH

Offices: 6-8 ACH

Workshops/Garages: 15-20 ACH

Laboratories: 15-20 ACH

Server rooms: 20-30 ACH

Applications

  • HVAC design: Sizing air handlers, fans, and blowers
  • Ventilation: Ensuring adequate fresh air supply
  • Cooling: Determining air flow for air conditioning
  • Heating: Calculating warm air distribution
  • Indoor air quality: Removing pollutants and odors
  • Industrial: Dust collection, fume extraction
  • Grow rooms: Plant ventilation and climate control

Tips for CFM Calculations

  • Higher ACH improves air quality but increases energy costs
  • Consider ceiling fans can improve air circulation without full air exchange
  • Bathrooms and kitchens need higher ACH due to moisture and odors
  • Temperature rise for heating typically 15-25°F, for cooling 15-20°F
  • Account for duct losses - add 10-20% to calculated CFM
  • Verify fan specifications match both CFM and static pressure requirements
  • Local building codes may specify minimum ventilation rates
See also
ENGINEERING CALCULATORS
WUTOOLS