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 a:b: W = diagonal × a / √(a² + b²). Rounded factors are 0.8716 for 16:9, 0.8480 for 16:10, and 0.8 for 4:3. The calculator uses the unrounded conversion. The throw ratio is unitless, so D and W must use the same length units.
Throw Ratio Reference Tables
These rounded reference values are a general guide. Category names and boundaries vary by manufacturer; they do not establish whether a particular projector or lens fits your installation.
| 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. The unrounded required ratio is about 1.49155173:1, so a range containing only the rounded value 1.5 does not establish a fit. Check the exact projector’s throw chart, reference point, zoom/focus limits, supported image size and aspect setting.
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? Use the lens-to-screen reference point and measurement diagram specified by the manufacturer for the exact projector or lens. Do not substitute the back of the case; ultra-short-throw models may need a model-specific placement diagram.
Does throw ratio depend on aspect ratio? The definition remains lens-to-screen distance divided by image width. Aspect ratio determines height and diagonal for a given width. Use the projector or lens manufacturer’s documented aspect setting and optical image width; letterboxing or cropping can make active content narrower than the optical image.
Can I move the projector closer to make a bigger image? At a fixed throw ratio, moving closer makes the image smaller, not bigger. At a fixed distance, a lower throw ratio produces a larger image. A zoom lens can change the ratio only within its documented range, focus limits and supported image sizes.
