Projector Throw Distance

Calculate a projector's mounting distance from the image size, or the image size from the distance, using the throw ratio (fixed or with a zoom range) and the aspect ratio. All in your browser.

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Throw distance

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Image width

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Image height

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Diagonal

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Distance —

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How it is calculated · throw ratio and aspect

1. The throw ratio is the distance divided by the image width (not the diagonal): throw = distance / width.

2. Width and height come from the diagonal and the aspect: width = diagonal · aspW / √(aspW² + aspH²) and height = diagonal · aspH / √(aspW² + aspH²). At 16:9 the width ≈ 0.8716 · diagonal and the height ≈ 0.4903 · diagonal.

3. Distance from size: distance = throw · width. Size from distance: width = distance / throw, then diagonal = width / (aspW / √(aspW² + aspH²)).

4. With a throw range (zoom) there is a minimum and maximum distance (or size). Conversion: 1 in = 0.0254 m.

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How it works

The calculator solves the typical projector-installation problem: at what distance to mount it to get a given image size (mode A), or what image size you get from a fixed distance (mode B). It works with the projector throw ratio, fixed or with a zoom range (for example 1.2–1.5:1), and with the aspect ratio: 16:9, 16:10, 4:3 or 2.35:1, converting between inches, meters and feet (1 inch = 0.0254 m).

The key detail is that the throw ratio is defined against the image width, not the diagonal: throw = distance ÷ width. Width comes from the diagonal and the aspect via width = diagonal × aspW ÷ √(aspW² + aspH²); in 16:9 the width is ≈ 0.8716 × diagonal and the height ≈ 0.4903 × diagonal. With a zoom lens, the throw range yields a minimum and maximum distance (or size).

Example: 100-inch 16:9 screen with a 1.2–1.5:1 throw

The width of a 100″ diagonal in 16:9 is 100 × 0.8716 = 87.16″ = 2.21 m (height ≈ 1.25 m).
Minimum distance (zoom at 1.2): 1.2 × 2.21 = 2.66 m.
Maximum distance (zoom at 1.5): 1.5 × 2.21 = 3.32 m: the projector can be mounted anywhere between 2.66 and 3.32 m from the screen.

Frequently asked questions

How far should a projector be for a 100-inch image?

It depends on the projector throw ratio. With a standard 1.5:1 throw and a 16:9 screen, the distance is 1.5 × 2.21 m ≈ 3.3 m. A short-throw projector (0.5:1) achieves the same 100″ from just 1.1 m. The throw figure is listed on the projector datasheet.

Is the throw ratio calculated with the diagonal or the image width?

With the width, and this is the most common mistake: throw = distance ÷ image width. Since screens are sold by diagonal, you must convert first: in 16:9 the width is roughly 87% of the diagonal. Using the diagonal directly inflates distances by about 15%.

What is the difference between a short-throw and a standard-throw projector?

The throw ratio: standard throw runs around 1.2 to 2.0 (needs several meters of room), short throw drops below 1.0 (large image from about 1 m) and ultra-short throw reaches 0.25 or less (installed right against the wall). Short throw avoids presenter shadows but is more sensitive to surface irregularities.

What if my projector has zoom, which distance should I use?

A zoom lens gives a throw range, for example 1.2–1.5:1: any distance between the calculated minimum and maximum works, and the zoom fits the image to the exact size. Mounting near the middle of the range keeps adjustment margin in both directions.

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We take great care to keep every tool accurate and review it thoroughly; even so, we can't guarantee it is free of errors or take responsibility for how the results are used. We recommend double-checking anything critical.

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