Projector Screen Size Calculator

Every projector has a throw ratio printed in its specs. The throw ratio is the relationship between throw distance (lens to screen) and image width:

throw_ratio = throw_distance / image_width

If a projector has a throw ratio of 1.5 and you place it 10 ft from the wall, the image width is 10 / 1.5 = 6.67 ft.

From width, you get the diagonal using the aspect ratio:

image_height = image_width / aspect diagonal = sqrt(width^2 + height^2)

Common aspect ratios:

• 16:9 (1.778): modern HDTV, and what almost every projector and nearly all content uses
• 16:10 (1.6): older laptops and business projectors, slightly taller
• 4:3 (1.333): old televisions and presentation slides
• 2.35:1: cinema scope. Films shot this way fill a scope screen edge to edge, and everything else arrives with pillarboxing down the sides

Throw ratio categories:

• Long throw (1.8+): old conference room projectors, distant placement
• Standard throw (1.0 to 1.8): most home theater projectors
• Short throw (0.4 to 1.0): mounted close to the wall
• Ultra-short throw (under 0.4): cabinet placement directly below screen

For a 100-inch diagonal 16:9 image (87.2 inch wide), you need a throw distance of roughly:

• Long throw 2.0: 174 inches (14.5 ft)
• Standard 1.5: 131 inches (10.9 ft)
• Short throw 0.7: 61 inches (5.1 ft)
• Ultra-short 0.3: 26 inches (2.2 ft)

Practical considerations:

• Zoom lens projectors give you a range, not one fixed throw ratio. A 1.2x zoom at a 1.5 base ratio means anywhere from 1.5 to 1.8, so you have some freedom in where the projector sits.
• Vertical and horizontal lens shift add more. Shift moves the image without tilting the projector, which is how you get a square picture from an off-center mount instead of the trapezoid that keystone correction then has to crop away.
• Doubling the diagonal quarters the brightness. This is not the inverse square law, which is about distance; it is simply that doubling the diagonal quadruples the area, and the projector still puts out the same total lumens spread over four times as much screen. So a 200-inch image needs roughly four times the lumens of a 100-inch one to look equally bright, and this is the single most common reason a projector that looked fine in the shop disappoints at home on a bigger screen.
• Most people overshoot the screen. A 100-inch image at 12 feet is comfortable. The same 12 feet with a 150-inch screen means constantly moving your eyes to follow the action, which is tiring within an hour.