RVA grille calculator

Find a field Ak for a grille, register, or diffuser and the CFM that goes with it. Type your own areas and Ak; there's no manufacturer table here. Nothing is saved on this page.

Job (optional)

Unit / location (optional)

Tech (optional)

Quick: CFM, FPM, and open area

Enter CFM and FPM to get Ak (Ak = CFM ÷ FPM). Or leave one of them blank and give the open area, and the page fills in the missing number.

CFM (traversed)

Average FPM (RVA)

Open area from

Face width (in)

Face height (in)

Percent open (%)

Same grille model, different size (optional)

Uses the percent open from above: Ak = percent open × this grille's face area.

Face width (in)

Face height (in)

Multi-grille: Ak from a unit traverse

Traverse the unit or main duct for total CFM, then read every grille it serves with the RVA. Enter each grille's size (or area) and FPM.

Unit total CFM (traversed)

Number of grilles

#	W (in)	H (in)	Area (sq ft)	FPM	Ak (sq ft)	CFM

Matches our RVA-2 sheet: one open-area factor = (traversed CFM ÷ straight average of the grille FPMs) ÷ total grille area, then each grille's Ak = factor × its area and CFM = FPM × Ak.