🎥 Projector Throw Distance Calculator

Enter your desired screen size (16:9) and your projector's throw ratio range (from its spec sheet) to find how far to mount it.

Desired screen diagonal (inches)

Throw ratio (minimum)

Throw ratio (maximum)

How the mounting distance is worked out

Throw ratio is defined against screen width, so the diagonal you enter is converted first:

screen width  = diagonal × 0.872        (16:9)
near distance = screen width × minimum throw ratio
far distance  = screen width × maximum throw ratio

The defaults work through as: a 100 in 16:9 screen is 87.2 in wide, or 7.27 ft, so a 1.4-1.6 throw ratio puts the lens between 10.2 ft and 11.6 ft from the screen. That span is the projector's zoom range off its spec sheet, not a tolerance: any distance inside it gives the full 100 in image.

Reading the spec sheet and placing the lens

Aim for the middle of the zoom range. Lenses are sharpest away from either extreme, the wide end passes the most light, and mounting at exactly 10.2 ft leaves no adjustment.
The 0.872 constant is 16:9 only. For a 2.35:1 scope screen the width is the diagonal × 0.920, so convert by hand before using this.
Vertical position is a separate spec. Throw ratio fixes distance, not height - lens shift range or a fixed offset percentage decides where the image lands relative to the lens axis.
Enter the smaller ratio first. Nothing sorts them, so swapped values print the range backwards.

This is geometry only - no brightness, and no screen or room gain assumed. Brightness is (lumens × screen gain) / screen area; that 100 in screen is 29.7 sq ft, against a SMPTE target near 16 foot-lamberts in a dark room. Calibrated modes give well under the rated lumens, so judge that from measured output rather than the box.

Frequently asked questions

How far should a projector be from a 100 inch screen?

It depends on the lens. A 1.4-1.6 throw ratio needs 10.2 to 11.6 ft, a 0.8 short-throw model sits at 5.8 ft, and a 2.0 long lens at 14.5 ft.

Is throw ratio measured against the screen width or the diagonal?

Width. Throw ratio is throw distance divided by image width, which is why the tool converts your diagonal first. Using the diagonal directly puts the projector about 15% too far back.

Can I use this for a 2.35:1 CinemaScope screen?

Not directly - the width conversion here is fixed at 16:9. Multiply a scope diagonal by 0.920 to get its width, then multiply that by your throw ratios.