Projector Calculators
Projector lumens vs screen size.
Enter the projector lumens, the screen width and the screen gain to get the screen brightness in foot-lamberts and nits, and the lumens you would need to hit a target. This is an ideal figure: lamp ageing, lens loss, picture modes and ambient light all lower it. Runs in your browser; nothing is sent or stored.
Inputs
Result
Fill the form and press Calculate.
Worked example
A 2,000 lumen projector on a 100 in wide 16:9 white screen (gain 1.0): the width is 100 / 12 = 8.33 ft and the height 4.69 ft, so the area is 39.06 sq ft. Brightness = 2,000 x 1.0 / 39.06 = 51.2 fL, which is 175 nits (fL x 3.426). To reach 16 fL the same screen needs 39.06 x 16 / 1.0 = 625 lumens.
How it works
fL = lumens x gain / screen area in square feet. The Foot-lambert - Wikipedia article gives the luminance of a diffuse surface in foot-lamberts as the illuminance in foot-candles times its reflectivity. A foot-candle is one lumen per square foot. The Projection screen - Wikipedia article describes gain as a measure of reflectivity compared with a reference white screen, so a white matte screen of gain about 1 has a reflectivity near 1. One foot-lambert is 3.426 candela per square meter.
The Foot-lambert - Wikipedia article says SMPTE 196M recommended a screen luminance of 16 foot-lamberts for commercial movie theaters (open gate), and that the current revision specifies 55 nits. That is a cinema figure, so use it as a reference point and not a rule for a home room.
Sources: Foot-lambert - Wikipedia; Projection screen - Wikipedia. Each opened 2026-10-08.
Planning guide only, not professional advice. Figures are estimates from the inputs you enter.
FAQ
How many lumens do I need for a 100 inch screen?
For 16 fL on a 100 in wide 16:9 screen with gain 1.0, about 625 lumens in the ideal case. Real projectors lose some light, so the rated figure should be higher.
What is 16 foot-lamberts?
It is the screen luminance SMPTE 196M recommended for commercial movie theaters, measured open gate. The current revision specifies 55 nits, about 16 fL.
What does screen gain do?
Gain compares a screen to a reference white. A gain above 1 reflects more light toward the viewer, but over a narrower angle.
How do I convert foot-lamberts to nits?
Multiply by 3.426. 51.2 fL is about 175 nits.
Does this account for ambient light?
No. Only lumens, gain and screen area are used, so room light, lamp ageing and lens loss are not modelled.