HVAC Airflow Conversion Calculator
Air changes per hour describes how many room volumes are exchanged by ventilation in one hour. This calculator converts room size and a chosen ACH target into a simple airflow estimate.
How to use this calculator
- Enter internal floor area and an appropriate design ACH based on qualified guidance.
- Check that the input values use the same units and reporting period before comparing scenarios.
- Change one assumption at a time to see which input drives the result.
Formula and method
Room volume = floor area × ceiling height; airflow (m³/h) = volume × target ACH.
- Volume = 117 m³; required flow = 117 × 5 = 585 m³/h, approximately 344 CFM.
- Required ventilation depends on occupancy, contaminants, local standards, system balance, leakage and pressure. This estimate is not a code-compliance design.
Worked examples
Worked example
A 45 m² room with a 2.6 m ceiling and target of 5 air changes per hour.
Volume = 117 m³; required flow = 117 × 5 = 585 m³/h, approximately 344 CFM.
The target corresponds to about 585 m³/h for the stated room volume.
Understanding the result
The target corresponds to about 585 m³/h for the stated room volume.
Required ventilation depends on occupancy, contaminants, local standards, system balance, leakage and pressure. This estimate is not a code-compliance design.
Important notes
Enter internal floor area and an appropriate design ACH based on qualified guidance.
The displayed result uses the entered assumptions; validate important estimates against source measurements, specifications or qualified guidance.
Frequently asked questions
Does this size an HVAC unit?
No. It estimates one airflow relationship and does not perform a heating or cooling load calculation.
Why show CFM?
CFM is cubic feet per minute, a common airflow unit; the conversion is approximate based on standard unit definitions.
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Learn the method behind the number or compare the terminology before using the calculator.
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This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.