CFM Calculator: Air Changes and Ventilation Rate

How to use the CFM calculator

1. Measure the room or the space that shares one ventilation rate.
2. Enter air changes per hour. CFM equals ACH × volume in cubic feet ÷ 60. The default 6 ACH is a starting point you can edit, not a code-required rate.
3. Optionally turn on the ASHRAE 62.2 whole-house rate and enter floor area and bedrooms.

Size the duct that will carry the airflow on the duct size calculator. Planning heating and cooling capacity stays on the BTU calculator.

Air changes and the 62.2 equation

CFM from air changes is a volume conversion: one air change per hour on a 1,000 cu ft room is 1,000 ÷ 60 ≈ 16.7 CFM.

ASHRAE Standard 62.2’s continuous whole-house mechanical ventilation rate, widely quoted by ACCA and by DOE Building America publications, is Q (CFM) = 0.03 × floor area in square feet + 7.5 × (bedrooms + 1). The “+ 1” estimates two people in the first bedroom and one in each additional bedroom. That rate is for the house, not for a single room’s ACH.

Worked examples: a 12×12 room and a 2,000 sq ft house

A 12 × 12 × 8 ft room is 1,152 cu ft. At 6 air changes per hour the airflow is 1,152 × 6 ÷ 60 = 115.2 CFM.

A 2,000 sq ft, three-bedroom house has a 62.2 continuous rate of 0.03 × 2,000 + 7.5 × 4 = 90 CFM.

Sources & assumptions

How this calculator gets its numbers. Full method: our methodology.

• CFM from air changes equals ACH × volume in cubic feet ÷ 60. Volume is length × width × height.
• The default 6 ACH is a CalcTheJob starting point you can edit, not a code-required room rate.
• The optional whole-house rate is ASHRAE 62.2 continuous mechanical ventilation: Q (CFM) = 0.03 × floor area (sq ft) + 7.5 × (bedrooms + 1). That rate is for the house, not a single-room ACH.
• This page does not size ducts or calculate a heating or cooling load.

Sources

1. Air Conditioning Contractors of America, 2016 Update for ASHRAE 62.2. States the 62.2 continuous whole-house rate as Qtot = 0.03 Afloor + 7.5 × (Nbr + 1), with a 2,000 sq ft, three-bedroom example of 90 CFM.
2. U.S. Department of Energy, Building America, Building Science — Ventilation (ASHRAE 62.2). DOE Building America issue paper describing ASHRAE 62.2 whole-house mechanical ventilation, including 7.5 cfm per person plus 0.03 cfm per square foot, with occupancy taken as bedrooms plus one.

Last reviewed November 12, 2026. A measured airflow or a ventilation design for the house wins.