💨 CFM Calculator
Calculate cubic feet per minute (CFM) for HVAC systems
Air changes per hour vary by room type and usage
How to Use This Calculator
Enter Room Dimensions
Input the length, width, and height of the room in feet. Measure from wall to wall for accurate calculations.
Select Air Changes per Hour
Choose the appropriate ACH based on room type. Residential living rooms typically need 6 ACH, while bathrooms and kitchens need 10-15 ACH.
Calculate and Review
Click "Calculate CFM" to see the required cubic feet per minute. Use this value to select the appropriate fan or HVAC system for your space.
Formula
CFM = (Volume × Air Changes per Hour) / 60
Volume = Length × Width × Height
Where: CFM = Cubic Feet per Minute, ACH = Air Changes per Hour
Example: 20 ft × 15 ft × 9 ft room with 6 ACH
Step 1: Volume = 20 × 15 × 9 = 2,700 cubic feet
Step 2: CFM = (2,700 × 6) / 60 = 270 CFM
Example: 12 ft × 10 ft × 8 ft bathroom with 10 ACH
Step 1: Volume = 12 × 10 × 8 = 960 cubic feet
Step 2: CFM = (960 × 10) / 60 = 160 CFM
About CFM Calculator
The CFM (Cubic Feet per Minute) Calculator is an essential tool for HVAC professionals, contractors, and homeowners who need to determine the proper airflow requirements for ventilation systems. This calculator eliminates guesswork by providing precise CFM calculations based on room size and air changes per hour, helping you select the right fan or HVAC equipment for optimal air quality and comfort.
When to Use This Calculator
- HVAC Sizing: Determine CFM requirements for heating and cooling systems
- Ventilation Planning: Calculate exhaust fan requirements for bathrooms and kitchens
- Air Quality: Ensure proper air circulation for healthy indoor environments
- Ductwork Design: Size ductwork based on required CFM
- Fan Selection: Choose appropriate fans for ventilation systems
Why Use Our Calculator?
- ✅ Accurate Calculations: Precise CFM calculations using standard HVAC formulas
- ✅ Air Change Standards: Pre-configured ACH values for different room types
- ✅ Multiple Units: Shows CFM, cubic meters per hour, and liters per second
- ✅ Time Savings: Instant calculations eliminate manual math and lookups
- ✅ Easy to Use: Simple input fields for room dimensions and ACH
Understanding Air Changes per Hour
Air Changes per Hour (ACH): ACH indicates how many times the entire volume of air in a room is replaced per hour. Higher ACH values mean better ventilation but may require larger or more fans. Different rooms have different ACH requirements based on their use and air quality needs.
Typical ACH Values: Storage rooms (2 ACH), bedrooms (4 ACH), living rooms (6 ACH), offices (8 ACH), kitchens (10 ACH), bathrooms (10-15 ACH), workshops (12 ACH), and clean rooms (20+ ACH). These values ensure adequate ventilation for comfort and health.
Tips for Best Results
- Measure Accurately: Use accurate room measurements for precise CFM calculations
- Consider Room Type: Select appropriate ACH based on room usage and ventilation needs
- Account for Multiple Rooms: Calculate CFM for each room separately if using multiple fans
- Add Safety Margin: Consider adding 10-20% extra CFM for safety and future needs
- Check Local Codes: Verify local building codes for minimum CFM requirements
Frequently Asked Questions
What is CFM?
CFM stands for Cubic Feet per Minute, which measures the volume of air moved per minute. It's the standard unit for measuring airflow in HVAC systems and fans.
How do I calculate CFM for a room?
CFM = (Room Volume × Air Changes per Hour) / 60. First calculate room volume (length × width × height), then multiply by desired ACH, and divide by 60 to get CFM.
How many air changes per hour do I need?
It depends on room type: 2-4 ACH for storage/bedrooms, 6 ACH for living rooms, 8 ACH for offices, 10 ACH for kitchens/bathrooms, and 12-20 ACH for high-activity areas. The calculator provides pre-configured values for different room types.
What CFM do I need for a bathroom fan?
Bathrooms typically need 10-15 ACH, which usually translates to 50-150 CFM depending on bathroom size. For a standard 8×8×8 ft bathroom (512 cu ft), you'd need about 85-128 CFM.
Can I use this calculator for HVAC sizing?
Yes! This calculator helps determine CFM requirements for HVAC systems. However, HVAC sizing also considers heating/cooling loads, so consult an HVAC professional for complete system design.
How does CFM relate to fan size?
Larger rooms or higher ACH requirements need higher CFM fans. Common fan sizes: 50-80 CFM for small bathrooms, 100-150 CFM for medium rooms, 200-300 CFM for large rooms, and 400+ CFM for commercial spaces.