Calculate projector throw ratio, lens-to-screen distance, or image size from screen width or diagonal, aspect ratio, and an optional zoom-lens ratio range.
Throw Ratio Formula
- D = throw distance from the projector lens to the screen
- W = image width on the screen
Rearranged for the other two modes:
If you only know the diagonal, convert it to width using the aspect ratio. For 16:9, W = diagonal × 0.8716. For 16:10, W = diagonal × 0.8480. For 4:3, W = diagonal × 0.8. The throw ratio itself is unitless, so D and W must be in the same units.
Throw Ratio Reference Tables
Use these to sanity-check the calculator output against the type of projector you own or plan to buy.
| Category | Throw Ratio | Typical Use |
|---|---|---|
| Ultra-short throw | < 0.4 | Cabinet-mounted, lens inches from wall |
| Short throw | 0.4 – 1.0 | Small rooms, classrooms, gaming |
| Standard throw | 1.0 – 2.0 | Home theater, ceiling mount |
| Long throw | > 2.0 | Auditoriums, large venues |
| Screen (16:9 diagonal) | Image Width | Distance @ 1.2:1 | Distance @ 1.5:1 | Distance @ 2.0:1 |
|---|---|---|---|---|
| 80 in | 69.7 in | 7.0 ft | 8.7 ft | 11.6 ft |
| 100 in | 87.2 in | 8.7 ft | 10.9 ft | 14.5 ft |
| 120 in | 104.6 in | 10.5 ft | 13.1 ft | 17.4 ft |
| 150 in | 130.7 in | 13.1 ft | 16.3 ft | 21.8 ft |
Worked Example and FAQ
Example. You want a 120-inch 16:9 image and your projector sits 13 feet from the screen. Image width is 120 × 0.8716 ≈ 104.6 in, or 8.72 ft. Throw ratio = 13 / 8.72 ≈ 1.49:1. Any projector with a throw range that includes 1.5 will fit.
Does throw ratio change with zoom? Yes. Projectors with a zoom lens list a range, like 1.2–1.6:1. Lower numbers in the range produce a larger image at the same distance.
Where do I measure throw distance from? From the front of the projector lens to the screen surface, perpendicular to the screen.
Does throw ratio depend on aspect ratio? No. Throw ratio is always distance over image width, regardless of whether the image is 16:9, 16:10, or 4:3. Aspect ratio only matters when converting from a diagonal measurement.
Can I move the projector closer to make a bigger image? Only within the projector’s zoom range. Going below the minimum throw ratio means you need a different projector or a short-throw lens.
