Room CFM calculator

Choose a room type to use a practical air-changes-per-hour preset, or enter a specific ACH when a design brief, code, or engineer gives you one. The calculation accepts volume in cubic feet or cubic meters, shows the normalized volume, identifies whether the ACH came from a preset or an override, and returns a transparent formula you can check. It is a quick planning value for ventilation layouts, equipment comparisons, and early estimates rather than a substitute for a complete mechanical design.

Turn room volume and air changes into supply CFM

Air changes per hour describe how many times an airflow would replace a room's full air volume during one hour. Supply equipment, however, is commonly rated in cubic feet per minute. This calculator connects those two quantities with a direct conversion: multiply the room volume in cubic feet by the selected ACH, then divide by 60 minutes. For example, a 2,400 cubic foot bedroom at 6 ACH needs 240 CFM under this simple air-change method. If your volume is in cubic meters, the calculator first converts it to cubic feet using 35.3146667215 cubic feet per cubic meter. The returned normalized volume makes that conversion visible instead of hiding it. Enter the net room volume when possible, especially where a ceiling void or large permanently enclosed structure should not be treated as occupied air space. The result is the supply airflow associated with the stated ACH; it does not automatically add duct leakage, system diversity, pressurization offsets, or an equipment safety factor. Those adjustments belong in the broader design process.

Choose a room-type preset or enter the required ACH

Room type provides a convenient starting point when you do not already have a specified air-change target. The calculator uses fixed planning presets: 6 ACH for bedrooms and living rooms, 8 for offices and classrooms, 12 for kitchens and gyms, 10 for bathrooms and workshops, and 4 for storage rooms. These values make comparisons consistent, but they are not presented as universal code requirements. Actual ventilation criteria can depend on occupancy, floor area, contaminants, exhaust demand, climate, building classification, and local regulation. When a mechanical schedule, authority, client brief, or qualified designer specifies an ACH value, enter it in the air changes per hour field. That explicit value overrides the room preset, and the output labels its source as a user override. The room type remains in the result to preserve context. This distinction is useful in saved estimates: another reviewer can immediately see whether the airflow came from a general planning assumption or from a project-specific requirement. Always record the source of any project-specific ACH alongside the calculation.

Use the result as a transparent planning calculation

The calculated CFM is useful for early supply-register estimates, fan comparisons, rough duct planning, and checking whether an equipment schedule is in the right range. It is also helpful when comparing two scenarios: keep the room volume fixed and vary ACH, or keep ACH fixed and compare room sizes. Because the algorithm is deterministic, the same valid inputs always return the same rounded result. Still, an ACH calculation addresses only one part of ventilation design. It does not calculate outdoor-air requirements by person or floor area, heating and cooling loads, exhaust replacement, pressure relationships, filtration pressure drop, duct friction, diffuser throw, sound, or fan operating points. Kitchens, bathrooms, laboratories, healthcare spaces, and workshops may have dedicated exhaust or safety rules that govern the final design. Treat the output as a clearly stated airflow target under the air-change method, then reconcile it with all applicable requirements. For construction documents, life-safety applications, or regulated occupancies, have a qualified professional verify assumptions and select equipment using its rated performance at the actual system resistance.