Throw Distance Calculator
Work out how far the projector should sit from a known screen size and throw ratio
Throw distance = image width × throw ratio. For a 100-inch 16:9 screen the image width is about 2.21 m: a projector with a 1.5:1 throw ratio sits at about 3.32 m, and one with 1.2:1 at about 2.66 m. This page calculates the optical distance from the lens center to the image; installation adds the body length and ventilation clearance.
Throw distance calculation
Result
Mounting distance adds the body length (ceiling mounting) and rear ventilation clearance to this figure. For ceiling mounting, move the actual position back by about 0.3–0.5 m.
The two distances mean different things: throw distance is lens to image, viewing distance is eye to image. If the viewing distance is well below the suggestion, the image is large enough to require scanning left and right. Recommend a screen size from your room →
Screen size and throw distance reference
16:9 image, exact conversion. Distances are optical, in meters.
| Screen diagonal | Image width × height | Throw ratio 0.4:1 | Throw ratio 1.2:1 | Throw ratio 1.5:1 | Throw ratio 2.0:1 |
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Throw ratio categories
By throw ratio value, projector lenses are usually grouped into four categories. The ranges below are common industry groupings; refer to the product datasheet for any specific model.
Placed against the wall to cast a large image; common in laser TVs.
Suited to small rooms: a large image from close range, reducing shadows in the light path.
The most common type for home and business use; about 2.5 m projects a 100-inch image.
Most long-throw lenses are in the 1.5–1.9 range, suited to large rooms or where the projector must be hidden.
Category boundaries differ slightly between sources (for example, some put the ultra-short-throw limit at 0.6). The ranges above are a common grouping for reference.
FAQ
What is throw ratio?
Throw ratio = throw distance ÷ image width. It describes how wide an image a projector casts at a given distance: the smaller the ratio, the larger the image at the same distance. It is an optical parameter determined by the lens.
What is the difference between throw distance and mounting distance?
"Throw distance" is the optical distance from the lens center to the projected image and is the value used to calculate throw ratio. "Mounting distance" is the actual position of the projector on site: it adds the body length (lens to mount bracket for ceiling mounting) and the ventilation clearance required by rear-exhaust models, usually with an extra margin.
A zoom lens has a throw ratio range — how do I calculate it?
A range means the lens can zoom: at a fixed image width the throw distance can be adjusted between the two ends. Use the smaller throw ratio for the nearest position and the larger one for the farthest, and place the projector anywhere between them.
Why does the calculated distance differ from the actual result?
This tool calculates an ideal optical distance and does not account for keystone correction, lens shift or lens tolerance. Datasheet throw ratios usually carry a tolerance (for example ±5%), and keystone correction can slightly change image size. For precise installation, refer to the product datasheet and leave an adjustment margin.