CFM Calculator
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CFM ≈ room volume × ACH ÷ 60 — rough ventilation sizing.
Rates last reviewed: July 2026
Room size
Required CFM
134
1,344 cu ft · 6 ACH
- Volume (m³)
- 38.1
Related calculators
Air changes and CFM
Ventilation moves air through a space measured in cubic feet per minute (CFM). Air changes per hour (ACH) describes how many times the room volume is replaced each hour. CFM = volume (cu ft) × ACH ÷ 60.
Residential guidance often targets 0.35–0.5 ACH for general ventilation, higher for kitchens and baths during exhaust operation. Whole-house systems use different metrics — this is a room-level estimate.
Example: 12 ft × 14 ft × 8 ft = 1,344 cu ft at 6 ACH → 1,344 × 6 ÷ 60 = 134 CFM.
Official sources
Rates and formulas in this calculator reference the documentation below. Confirm current numbers on the source site before relying on them. Links do not imply endorsement by those organizations of Calcometry or this tool.
Common questions
What ACH should I use?
6 ACH is common for bath exhaust sizing examples; whole-house needs are lower. Check local mechanical code and product guides.
Is this for heating or cooling?
CFM applies to both airflow and ventilation. HVAC duct sizing also depends on load and velocity limits.