Throw Ratio Throw Ratio

What throw ratio measures

Throw ratio describes how far a projector must be placed from a screen to produce a given image width. It is defined as the throw distance (D) divided by the resulting image width (W): throw ratio = D/W. Wikipedia states the same relationship as R = D / W, where D is the distance to the screen and W is the screen width, assuming the projected image fills the screen fully. BenQ describes it from the other direction as the image width (W) in relation to the throw distance (D), but the underlying formula they publish is identical (D/W = 2/1 for a 2.0 ratio).

Because the ratio is unitless, it scales to any screen size: it expresses how many units of distance are needed per unit of image width, not a fixed distance.

Reading the number

A throw ratio of 2.0 (commonly cited as the most typical projector throw ratio) means the projector needs to be 2 feet away from the screen for every 1 foot of image width (D/W = 2/1 = 2.0). A lower ratio means the projector sits proportionally closer to the screen to fill the same width; a higher ratio means it sits proportionally farther away.

Zoom lenses are specified with a throw-ratio range rather than a single fixed value, spanning the lens's minimum to maximum zoom settings. Wikipedia's own example illustrates this: a lens with a throw ratio of 1.2–3.0 used on a 100-inch-wide screen, where the projector could be placed anywhere within the distance range that ratio spread implies while still filling that screen width.

Short throw and the 0.4 threshold

A projector is generally classified as a short throw projector when its lens has a throw ratio of 0.4 (distance/width) or less. This threshold is given by ProjectorCentral and independently corroborated by Wikipedia, which states that a lens with a throw ratio of 0.4 or less would be positioned relatively close to the screen and considered short throw. This 0.4 cutoff functions as a working industry convention rather than a figure defined by a formal standards body.

Worked example

To find the required throw distance for a target image width, multiply the desired width by the throw ratio. With a 2.0:1 throw ratio and a desired image width of 5 feet, the required distance is 5 × 2 = 10 feet.

BenQ illustrates the standard-throw versus short-throw distinction using two of its own models at a 100-inch image size: the X3100i, a standard throw projector, needs 8.2 feet of throw distance to produce a 100-inch image, while the X500i, a short throw projector, needs only 5 feet for the same 100-inch image. These are manufacturer-published figures for BenQ's own lineup rather than independently lab-measured values, but they show concretely how a lower throw ratio compresses the distance needed for an equivalent image size.

Common confusions

Throw ratio is not the same thing as throw distance. Throw distance is a specific measurement (in feet or meters) between the projector and the screen for a particular installation; throw ratio is the fixed proportional relationship (D/W) that, combined with a target image width, is used to calculate that distance. The same throw ratio produces different throw distances depending on the screen size chosen.

There is no confirmed formal standards-body (CTA, ANSI, or ISO) definition of throw ratio; the term is used consistently across manufacturer literature (BenQ), measurement-focused calculators (ProjectorCentral), and reference sources (Wikipedia), but as an industry convention rather than a codified specification.