Air Changes per Hour Calculator
Calculate air changes per hour with explicit inputs and a worked example.
Formula
- Use the units shown beside each field.
- Results update automatically whenever you change an input.
- Displayed values use up to four decimal places, or scientific notation for very small or large numbers. Calculations use standard floating-point arithmetic; exact integer and fraction tools identify their own precision rules.
- Ideal perfectly mixed room model. Does not determine the ventilation required by a building code.
Example Calculation
- Air flow: 300 m³/h
- Room volume: 75 m³
300 m³/h in a 75 m³ room gives 4 air changes per hour.
Frequently asked questions
How do I use this calculator?
Enter air flow, room volume. The result updates automatically. Use Reset to restore the example values.
What method does it use?
ACH = hourly flow / room volume. Ideal perfectly mixed room model. Does not determine the ventilation required by a building code.
Why might a rounded result differ?
The calculation keeps full numeric precision internally, then rounds the displayed result. Rounding intermediate steps by hand can produce a slightly different answer.
Are my inputs saved online?
No. This calculator processes your inputs in your browser. A recently used list stores only calculator names on this device, not your entered values.
Check the assumptions and units before using this result. Read about calculation methods.