Tools

Projector Unit Conversions

The quick math behind every projector spec sheet. Type in any box and the rest follow.

Screen brightness

Foot-lamberts

Nits

Reference: SDR in a dark room targets about 14–16 ftL (48–55 nits).

Room light

Foot-candles

Lux

A dim living room is roughly 3–10 foot-candles on the screen. Daylight through windows can exceed 50.

Length

Inches

Feet

Centimeters

Meters

Lumens → screen brightness

Projector lumens (ANSI)

Screen diagonal (in)

Screen gain

Foot-lamberts

Nits

Throw ratio → distance

Throw ratio

Image width (in)

Throw distance (ft)

Lens to screen. For a zoom lens, run it twice: once with each end of the ratio range.

Viewing angle

Image width (in)

Seat distance (ft)

Viewing angle (°)

Image width (in)

Target angle (°)

Seat distance (ft)

SMPTE recommends at least 30°; THX calls 36–40° the sweet spot.

Contrast ratio

Contrast (e.g. 2000)

Stops

Black = % of white

Each stop doubles the ratio. A 2000:1 projector resolves about 11 stops.

A note on lumen units

ANSI and ISO lumens both use a 9-point measurement and are roughly comparable. "LED lumens" and "light source lumens" are not standards — treat them as marketing. When a calculator asks for lumens, it means ANSI unless it says otherwise.