Calculate how many supply diffusers or grilles are needed from total CFM, diffuser size, and target throw. Includes standard size CFM capacity table.
| Space Type | ft²/Diffuser | CFM/Diffuser |
|---|---|---|
| Open office | 150–200 | 150–250 |
| Private office / classroom | 100–150 | 100–200 |
| Retail / open plan | 200–300 | 200–400 |
| Corridor / low-load | 200–400 | 50–150 |
| Perimeter (heating) | — | size for 550–700 FPM NC-30 |
This diffuser count estimator gives a fast first pass at how many supply diffusers, grilles, or registers a space needs. Enter the total supply airflow in CFM and a target airflow per diffuser — either typed directly or filled from the standard-size dropdown — and the tool returns the number of outlets required, the CFM each will carry, and, if you provide a floor area, the resulting square feet and approximate spacing per diffuser.
Splitting the airflow across enough outlets keeps neck velocity, throw, and noise in check while distributing air evenly across the ceiling. The standard size capacities and the spacing check help you sanity-test a layout before committing to a reflected ceiling plan, but final diffuser selection should always confirm throw and NC against manufacturer data.
| Diffuser count | N = ⌈ Qtotal (CFM) ÷ Qper (CFM) ⌉ |
| Area per diffuser | Aper = Floor area (ft²) ÷ N |
| Approx. spacing | s ≈ √Aper (ft) |
The count divides total airflow by the airflow per diffuser and rounds up (the ceiling function ⌈ ⌉) so no outlet is overloaded. When a standard size is selected, the target CFM per diffuser defaults to the midpoint of that size's rated range, (min + max) ÷ 2. Square-grid spacing is approximated as the square root of the floor area per diffuser. The tool flags spacing outside roughly 100–300 ft² per diffuser. Capacity ranges and the spacing band follow standard ASHRAE / manufacturer diffuser-selection practice; verify throw, drop, and noise (NC) against the manufacturer's data.
This calculator handles one step. AIM Works runs the complete MEP design workflow — thermal load calculations, duct & pipe networks, equipment selection, code compliance, and an AI design assistant — in one tool.
Results are design estimates for preliminary sizing. Verify final designs against applicable codes and standards — engineering judgment and a licensed professional engineer’s review are required.