CFM Calculator

CFM Calculator for Room Ventilation

The CFM Calculator estimates required airflow in cubic feet per minute (CFM) from room size and air changes per hour (ACH). Use it to size exhaust fans, supply fans, and HVAC ventilation for kitchens, bathrooms, offices, and workshops.

CFM formula

Required airflow depends on room volume and how often the air should be replaced:

$$\text{CFM} = \frac{\text{Floor area} \times \text{Ceiling height} \times \text{ACH}}{60}$$

ACH means how many times the entire room air volume is replaced per hour. One ACH replaces the full room volume once every 60 minutes.

Typical ACH values

Bedrooms often need 5-6 ACH. Kitchens and living rooms need 6-8 ACH. Bathrooms need 6-7 ACH or higher with dedicated exhaust fans. Workshops, copy rooms, and commercial kitchens may need 10-60 ACH depending on contaminants.

Example: kitchen ventilation

A 250 sq ft kitchen with 8 ft ceilings and 8 ACH needs: $250 \times 8 \times 8 / 60 \approx 267$ CFM. Round up to the next standard fan size (about 270 CFM).

Related tools: Air Changes Per Hour Calculator, AC Tonnage Calculator, and Boiler Size Calculator.