CFM Calculator — Room Airflow & HVAC Ventilation
Enter a room's length, width, ceiling height and target air changes per hour (ACH) to find the CFM your fan, air handler or ventilation unit must deliver.
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Cubic feet per minute needed to achieve the target ACH
240 CFM
2.400 ft³- 1
Room volume
20 × 15 × 8 ft = 2.400 ft³ - 2
Required airflow
2.400 × 6 ÷ 60 = 240Volume × air changes per hour, divided by 60 converts to per-minute.
Como esta calculadora funciona?
Multiply room volume (L × W × H in feet) by air changes per hour, then divide by 60 to get the required CFM. A 1,440 ft³ bedroom at 5 ACH needs 120 CFM. Multiply CFM by 1.699 to convert to m³/h (CMH) for European specs. All results assume ideal steady-state airflow with no duct losses.
Fórmula
How this is calculated
CFM stands for cubic feet per minute — the standard North American unit for measuring how much air a fan, air handler or ventilation system moves in one minute. The required CFM for a room is set by two things: the room's volume and how many complete air-volume replacements you want per hour (ACH, air changes per hour). Multiplying volume by ACH gives cubic feet per hour; dividing by 60 converts that to the CFM your equipment must deliver.
ACH targets vary by room type. Bedrooms typically need 4–6 ACH for comfort ventilation, living rooms and offices 6–10, kitchens 10–15, and bathrooms 8–12. These are general guidelines — local building codes (such as ASHRAE 62.1 for commercial or 62.2 for residential), occupancy counts and specific air-quality or pressurisation requirements may demand higher rates. Room dimensions must be in feet; if you have metres, multiply each by 3.281 before entering.
The CMH (cubic metres per hour) result enables comparison with European equipment specifications: 1 CFM ≈ 1.699 m³/h. All results assume steady-state delivery — duct losses, filter resistance and fan efficiency derating are not modelled and must be added by a qualified HVAC engineer for code-compliant designs.
Perguntas frequentes
Volume = 12 × 15 × 8 = 1,440 ft³. At 5 ACH: CFM = (1,440 × 5) ÷ 60 = 120 CFM. At 6 ACH you need 144 CFM. Choose a fan or air handler rated at or above that CFM at your duct static pressure.
Multiply CFM by 1.699011. So 100 CFM ≈ 169.9 m³/h. To go the other way, divide m³/h by 1.699. This is exact because 1 ft³ = 0.0283168 m³ and 1 min = 1/60 hr.
Kitchen range hoods typically target 10–15 ACH for general ventilation, but the HVI (Home Ventilating Institute) rates range hoods in CFM rather than ACH. A rough rule is 100 CFM per linear foot of range width for light cooking; heavy cooking or professional ranges may need 200+ CFM/ft.
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TG we-Calculate Editorial Team. (2026). CFM Calculator — Room Airflow & HVAC Ventilation [Online calculator]. TG we-Calculate. https://we-calculate.com/pt/calculator/cfm-calculator
TG we-Calculate Editorial Team. "CFM Calculator — Room Airflow & HVAC Ventilation." TG we-Calculate. 2026. https://we-calculate.com/pt/calculator/cfm-calculator.
TG we-Calculate Editorial Team, "CFM Calculator — Room Airflow & HVAC Ventilation," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/pt/calculator/cfm-calculator
@misc{wecalculate_cfm_calculator, title = {CFM Calculator — Room Airflow & HVAC Ventilation}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/pt/calculator/cfm-calculator}}, year = {2026}, note = {TG we-Calculate} }
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