Projector Throw Distance Calculator — Lens Ratio Math | TheaterOwl

The Projector Throw Distance Calculator multiplies a screen's 16:9 width by the projector's throw ratio to return the exact lens-to-screen distance needed to fill the image. Enter the screen size in inches and the throw ratio range published in the projector's spec sheet (commonly 0.5 to 2.5), and the tool gives the minimum and maximum mounting distances in feet and meters.

How it Works

Throw ratio equals throw distance divided by image width, so throw distance = screen width x throw ratio. The calculator first converts a 16:9 diagonal to width using width = diagonal x cos(arctan(9/16)), then applies the ratio. A 120-inch 16:9 screen (104.6 inches wide) with a 1.5 throw ratio needs 13.1 ft (4.0 m); a 0.5 UST lens needs only 4.4 ft (1.3 m).

Usage Scenarios

• Ceiling mounting a long-throw business projector in a 20 ft room and verifying the lens lands inside its 1.4 to 2.3 throw range
• Choosing between a short-throw and an ultra-short-throw model for a 100-inch screen in a 10 ft x 12 ft media room
• Wall mounting a UST laser projector below a 120-inch ALR screen and confirming the 0.25 throw ratio leaves the right gap
• Retrofitting an older projector into a new room and checking the existing wall-to-screen distance still hits the lens's minimum throw

How to Use the Projector Throw Distance Calculator

Find your projector's throw ratio in its manual or manufacturer website. This is the ratio of throw distance to screen width. For example, a 1.5 throw ratio means the projector must be placed 1.5× the screen width from the screen.

Standard throw projectors typically have ratios of 1.3–2.0. Short throw projectors range from 0.3–1.0. Ultra-short throw (UST) projectors have ratios below 0.3 and can sit directly below the screen.

The calculator uses a 16:9 aspect ratio to convert your diagonal screen size to width. If your screen has a different aspect ratio, the actual throw distance will differ slightly.

FAQ

What is a projector throw ratio?

Throw ratio is the relationship between lens-to-screen distance and image width: throw ratio = distance / width. A 1.5 throw ratio means the projector sits 1.5 times the image width away from the screen.

How far should a projector be from a 120 inch screen?

A 120-inch 16:9 screen is about 104.6 inches (8.72 ft) wide. With a 1.5 throw ratio you need 13.1 ft of throw, with a 1.0 ratio you need 8.7 ft, and an ultra-short-throw 0.25 ratio needs only 2.2 ft.

What throw ratio is considered short throw versus long throw?

Ultra-short-throw (UST) is below 0.4, short-throw is 0.4 to 1.0, standard throw is 1.0 to 2.0, and long-throw is above 2.0. UST projectors sit just inches from the screen, while long-throw models are used in conference rooms and large theaters.

Can I use digital keystone to fix the wrong throw distance?

You can, but it scales the image down and reduces effective resolution and pixel accuracy. The correct fix is to mount the projector at the throw distance the lens is designed for, then use optical lens shift for fine alignment.

Does throw distance change with aspect ratio?

Yes. Throw ratio is tied to image width, so a 2.35:1 screen of the same diagonal is about 12 percent wider than a 16:9 screen and therefore needs about 12 percent more throw distance for the same lens setting.