What this calculator does
Air changes per hour works out how many times an hour a ventilation system replaces a room's air. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaACH = airflow rate (m³/h) ÷ room volume (m³)
The inputs explained
| Field | What to enter |
|---|---|
| Room length (m) | A number, measured in m. Starts at 5. |
| Room width (m) | A number, measured in m. Starts at 4. |
| Ceiling height (m) | A number, measured in m. Starts at 2.7. |
| Airflow rate (m³/h) | A number, measured in m³/h. Starts at 150. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with room length
Every other input is held at the calculator’s starting values while room length varies. Select any row to load that scenario into the calculator.