How to calculate projector throw distance
Throw distance = image width × throw ratio. Here is the step-by-step formula, the 16:9 diagonal-to-width conversion, and a ready table by throw ratio.
Throw distance = image width × throw ratio. First convert the screen diagonal to width (for 16:9, width = diagonal × 0.872), then multiply by the projector's throw ratio. For a 100-inch screen (87 inches wide) and a 1.5 throw ratio: 87 × 1.5 = 131 inches, about 11 feet.
Two steps: get the image width from the diagonal, then apply the throw ratio. For a 16:9 screen, width = diagonal × 0.872 and height = diagonal × 0.490. Measure from the lens, and leave roughly a foot for the projector body and cables behind it.
Throw distance by throw ratio (for 100- and 120-inch screens)
| Throw ratio | 100″ screen | 120″ screen |
|---|---|---|
| 0.25 | 1.8 ft | 2.2 ft |
| 0.50 | 3.6 ft | 4.4 ft |
| 0.80 | 5.8 ft | 7.0 ft |
| 1.00 | 7.3 ft | 8.7 ft |
| 1.20 | 8.7 ft | 10.5 ft |
| 1.50 | 10.9 ft | 13.1 ft |
| 2.00 | 14.5 ft | 17.4 ft |
Frequently asked questions
Related guides
What is throw ratio?
Throw ratio is the projection distance divided by the image width: throw ratio = distance ÷ width. A 1.5 throw ratio means the projector sits 1.5× the screen width away — so for a 100-inch 16:9 screen (87 inches wide), about 11 feet back. A lower ratio sits closer; a higher ratio needs more room.
GuidesProjector screen size guide
A screen's "size" is its diagonal, but placement depends on width. For a 16:9 screen, width = diagonal × 0.872 and height = diagonal × 0.490. So a 100-inch screen is 87 inches (221 cm) wide and 49 inches (124 cm) tall.
GuidesProjector ceiling mount height
Mount the projector so its lens lines up with the top of the image when the projector has 0% offset (most do), then fine-tune with lens shift. A 100-inch 16:9 image is 49 inches (124 cm) tall, and the screen bottom usually sits 24-36 inches (60-90 cm) above the floor for seated eye level.
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