What is throw ratio?
Throw ratio is the projection distance divided by image width. Here is what it means, the formula, typical ranges, and how it sets how far a projector sits.
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.
Throw ratio is the single number that determines where a projector can sit. It is fixed per projector (or a small range if it has a zoom lens), and it always refers to image WIDTH, not the diagonal. Ultra-short-throw projectors have ratios below 0.4 and sit inches from the wall; standard projectors are around 1.0–2.0 and sit across the room.
Throw ratio bands and where each sits (100-inch screen)
| Type | Throw ratio | 100″ screen | Models | Example |
|---|---|---|---|---|
| Ultra-short-throw (UST) | < 0.4 | 1.8 ft | 20 | Epson EpiqVision Ultra LS800 |
| Short throw | 0.4 – 1.0 | 5.1 ft | 8 | BenQ X500i |
| Standard / long throw | 1.0 – 2.0 | 10.9 ft | 51 | Epson Home Cinema 2350 |