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Air Changes Per Hour Calculator
Ctrl+D to bookmark this toolCalculate ACH from flow rate and room volume, or find the required flow rate from target ACH.
or enter dimensions
Air changes per hour—
Formula: ACH = (Q × 3600) / V (Q in m³/s, V in m³)
or enter dimensions
Required flow rate
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All units
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Formula: Q = ACH × V / 3600 (Q in m³/s, V in m³)
Common air change rates
Typical values from CIBSE Guide A & Guide B. Verify against project-specific requirements.
| Space Type | Typical ACH |
|---|---|
| Office | 4 – 6 |
| Classroom | 5 – 8 |
| Hospital ward | 6 |
| Operating theatre | 15 – 25 |
| Kitchen (commercial) | 15 – 30 |
| Laboratory | 6 – 15 |
| Toilet / WC | 6 – 10 |
| Plant room | 5 – 10 |
| Car park | 6 – 10 |
| Retail | 3 – 6 |
MEP Desk calculates air changes automatically from your room data — with 61 engineering calculators across ventilation, heating, electrical, and more.