Grille & Register Size Calculator

Inputs

Airflow (Q)

Airflow through the grille, register or diffuser.

m³/h

Target face velocity (v_f)

Target velocity through free area. Lower is quieter; higher needs catalog noise and pressure-drop checks.

m/s

Free-area ratio (FAR)

Open free area divided by nominal grille face area. Catalog values vary by grille type and damper position.

Target aspect ratio (W/H)

Width divided by height for the suggested rectangular grille.

Installed width (W_i)

Width of an existing or candidate grille for the face-velocity check.

Installed height (H_i)

Height of an existing or candidate grille for the face-velocity check.

Default result

Required nominal area(A_nom)

0.064m²

Pass

nominal face area after free-area ratio

Also computed

Suggested width(W)357.8mm

Suggested height(H)178.9mm

Installed face velocity(v_i)3.556m/s

higher face velocity; check noise and pressure drop

Required free area(A_free)0.048m²

Installed free area(A_i)0.03375m²

Equivalent round diameter(D_eq)285.5mm

Method notes 3 notes

Free area = airflow / target face velocity. Nominal area = free area / free-area ratio.
The installed face-velocity check uses entered width × height × free-area ratio.
Final diffuser or grille selection should use manufacturer throw, NC/noise and pressure-drop catalog data at the design airflow.