| Space Type | Min ACH | Source |
|---|---|---|
| Office | 4–6 | ASHRAE 62.1 |
| Conference Room | 6–10 | ASHRAE 62.1 |
| Classroom | 6–8 | ASHRAE 62.1 |
| Exam Room (Medical) | 6 min | ASHRAE 170 |
| Patient Room | 6 min (2 OA) | ASHRAE 170 |
| Operating Room | 20 min (4 OA) | ASHRAE 170 |
| Laboratory | 6–10 (fume) | ASHRAE 62.1 |
| Commercial Kitchen | 15–60 | IMC Table 403.3 |
| Restroom (public) | 2 CFM/SF or 50 CFM/fixture | IMC 403.3 |
| Parking Garage | 0.75 CFM/SF | IMC 404 |
This air changes per hour calculator relates supply airflow, room volume, and ventilation rate. Choose what to solve for — ACH, CFM, or room volume — enter the other two values, and the tool returns the result plus the minutes required for one complete air change. A space-type selector shows the typical code or design target alongside your number.
Engineers use ACH to size or check ventilation against codes that specify air changes rather than CFM, and to translate between the two. The reference ranges draw on ASHRAE 62.1, ASHRAE 170 for healthcare, and the IMC, so you can quickly see whether a design meets the expectation for that occupancy.
| Air changes/hr | ACH = (CFM × 60) ÷ Volume (ft³) |
| Required airflow | CFM = (ACH × Volume) ÷ 60 |
| Room volume | Volume = (CFM × 60) ÷ ACH |
| Minutes per change | min/change = 60 ÷ ACH |
The factor 60 converts CFM (cubic feet per minute) to cubic feet per hour so it can be divided by the room volume. Recommended ranges follow ASHRAE 62.1 ventilation, ASHRAE 170 for healthcare spaces, and IMC Table 403.3; some line items (restrooms, garages) are specified as CFM per square foot or per fixture rather than ACH. Confirm the governing rate against the code adopted in your jurisdiction.