Bathroom CFM Calculator
Ventilation airflow for a bathroom at the recommended 8 air changes per hour.
Run 20 minutes past showering (humidity sensor) to kill mould growth.
Formula
Bathroom CFM Calculator is a free bathroom cfm for HVAC designers, technicians and energy auditors — instant, accurate and 100% client-side, with the governing formula and reference shown next to the result so the number can be defended, not just quoted.
About Bathroom CFM Calculator
Ventilation airflow for a bathroom at the recommended 8 air changes per hour. The calculation implements Q = room volume × 8 ACH (ASHRAE 62.1/62.2 ventilation rates). Run 20 minutes past showering (humidity sensor) to kill mould growth.
How to use Bathroom CFM Calculator
- 1Enter Length in m.
- 2Enter Width in m.
- 3Enter Ceiling height in m.
- 4Enter Air changes per hour in ACH.
- 5Read Required airflow, Airflow instantly — no submit button needed.
- 6Need US units? Flip the SI/Imperial toggle and every field converts.
Why use Bathroom CFM Calculator?
- ✓Implements the standard formula — Q = room volume × 8 ACH
- ✓Reference cited on-page: ASHRAE 62.1/62.2 ventilation rates
- ✓One-click SI ⇄ Imperial toggle — values convert in place, physics stays in SI
- ✓Runs entirely in your browser — nothing uploaded, free forever
Frequently asked questions
What formula does the Bathroom CFM Calculator use?+
It computes Q = room volume × 8 ACH, per ASHRAE 62.1/62.2 ventilation rates. The formula is displayed under the result.
What should I keep in mind when using this calculator?+
Run 20 minutes past showering (humidity sensor) to kill mould growth.
Is this based on ASHRAE methods?+
The calculations follow the standard ASHRAE/ISHRAE formulations cited under the result, simplified where industry practice does the same. For permit-grade design, confirm with the full code procedure.
Is the Bathroom CFM Calculator free to use?+
Yes — completely free, no sign-up, no limits. It runs client-side in your browser, so inputs stay private and results are instant even on slow connections.
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