Estimate the number of supply diffusers from total airflow, diffuser size, and room area.
| 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) | — | select for throw down the glass from catalog data |
Doing this for a whole building? See this step inside a connected AIM Works project — loads, ventilation, equipment, and Design Review in one place.
Book a Demo →This diffuser count estimator gives a fast first pass at how many ceiling supply diffusers a space needs. Enter the total supply airflow in CFM and a target airflow per diffuser — either typed directly or filled from the neck-size dropdown — and the tool returns the number of outlets required, the CFM each will actually carry once the count is rounded up, 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) ⌉ |
| Actual CFM each | Qeach = Qtotal ÷ N |
| 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. Choosing a neck size fills the target with the midpoint of that size’s range, (min + max) ÷ 2, and you can type any other target; the tool flags a split that falls outside the selected size’s range. The CFM per diffuser shown is the actual split, Qtotal ÷ N. Square-grid spacing is approximated as the square root of the floor area per diffuser, and spacing outside roughly 100–300 ft² per diffuser is flagged. The capacity ranges are typical catalog values for square-plaque and louvered ceiling diffusers (about 250–600 fpm neck velocity) and the spacing band is a rule of thumb — verify throw, drop, and noise (NC) against the manufacturer’s data. For sidewall registers, return and transfer grilles use the Grille & Register Sizing tool.
AIM Works brings peak loads, ASHRAE 62.1 ventilation, equipment and plant sizing, compliance checks, Design Review, and engineering deliverables into one connected mechanical design workspace.
Duct and pipe distribution sizing is planned for V2 — at launch, keep using this calculator for that step.
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.