Grille & Register Size Calculator

Inputs

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Airflow through the grille, register or diffuser.
cfm
Target velocity through free area. Lower is quieter; higher needs catalog noise and pressure-drop checks.
ft/min
Open free area divided by nominal grille face area. Catalog values vary by grille type and damper position.
Width divided by height for the suggested rectangular grille.
Width of an existing or candidate grille for the face-velocity check.
in
Height of an existing or candidate grille for the face-velocity check.
in

Results

Default result
Edit inputs
Required nominal area(A_nom)
0.6889ft²
Pass

nominal face area after free-area ratio

Also computed

Suggested width(W)14.09in

Suggested height(H)7.043in

Installed face velocity(v_i)Caution699.9ft/min

higher face velocity; check noise and pressure drop

Required free area(A_free)0.5167ft²

Installed free area(A_i)0.3633ft²

Equivalent round diameter(D_eq)11.24in

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.

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