Projector Calculator

Find your projector's screen width, screen height, and throw distance range from the screen diagonal, aspect ratio, and the projector's throw ratio.

Quick Facts

Formula
Throw ratio = throw distance / screen width
Rearranged: throw distance = throw ratio x screen width. Check the projector's manual for its throw ratio (a range for zoom lenses, one number for fixed lenses).

Your Results

Calculated
Throw distance range
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Projector lens to screen
Screen width
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Visible image width
Screen height
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Visible image height
Midpoint distance
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Center of the throw range

Ready

Enter screen size, aspect ratio, and throw ratio, then press Calculate.

About the Projector Calculator

This tool converts a screen size and a projector's throw ratio into two practical numbers: how big the picture will be, and how far from the screen the projector needs to sit. It uses the same throw-ratio math printed in every projector's spec sheet, so the result matches what a manufacturer's own placement guide would show.

The throw ratio formula

A projector's throw ratio is defined as throw ratio = throw distance / screen width, where both measurements use the same units (inches or feet). Manufacturers publish this as a single number for fixed-lens projectors (e.g., 1.5:1) or as a minimum-to-maximum range for zoom lenses (e.g., 1.2-1.5:1). Rearranging the formula gives the distance you actually need: throw distance = throw ratio × screen width. A short-throw projector has a low ratio (around 0.4-1.0) and sits close to the screen; a long-throw projector has a higher ratio (2.0 and up) and sits much farther back.

Getting screen width and height from the diagonal

Screens are sold by diagonal size, but the throw formula needs the width. For an aspect ratio of W:H, the diagonal is the hypotenuse of a right triangle with legs W and H, so by the Pythagorean theorem:

  • Screen width = diagonal × W / √(W² + H²)
  • Screen height = diagonal × H / √(W² + H²)

For the common 16:9 widescreen ratio, √(16² + 9²) ≈ 18.36, so a 100 inch diagonal screen works out to about 87.2 inches wide and 49.0 inches tall. Once the width is known, it is multiplied by the minimum and maximum throw ratio to get the full placement range.

How to use this calculator

  • Enter the screen's diagonal size in inches (measured corner to corner of the visible image, not the frame).
  • Choose the aspect ratio that matches your screen or content — 16:9 for most home theater and presentation content, 4:3 for older projectors and some classrooms, 21:9 for cinema-style ultra-wide setups.
  • Enter the minimum and maximum throw ratio from your projector's spec sheet. If your projector has a fixed (non-zoom) lens, enter the same value in both fields.
  • Press Calculate to see the screen dimensions and the distance range where the projector should sit for that screen size.

Practical context

The result tells you where the lens center should sit, measured perpendicular to the screen; it does not account for vertical or horizontal lens shift, keystone correction, or ceiling-mount offsets, which shift the usable range slightly. Always confirm the final placement against the specific throw-distance table in your projector's manual before drilling a mount or ordering a fixed screen.

Frequently Asked Questions

What is a projector's throw ratio?
Throw ratio is throw distance divided by screen width (both measured in the same units): throw ratio = distance / width. A projector's spec sheet lists this as a single number (fixed lens) or a range (zoom lens), such as 1.5:1 or 1.2-1.5:1. Rearranged, distance = throw ratio × width, which is how this calculator finds how far to place the projector.
How is screen width calculated from the diagonal?
For an aspect ratio of W:H, the diagonal, width, and height form a right triangle, so diagonal² = width² + height². Width = diagonal × W / √(W² + H²), and height = diagonal × H / √(W² + H²). For a 100 inch 16:9 screen this gives a width of about 87.2 inches and a height of about 49.0 inches.
Where do I find my projector's throw ratio?
Check the projector's spec sheet or manual, usually listed under "throw ratio" or "projection distance." Fixed-lens projectors list one number; zoom-lens models list a minimum and maximum. Enter the same value in both the minimum and maximum ratio fields if your projector has a fixed lens.

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