Projector Distance Calculator

The Science of Throw Ratios

The "Throw Ratio" is the fundamental constant in projector installation. It is a simple formula: Distance divided by Width (D/W). However, understanding the physics behind the lens glass is crucial for a professional setup.

1. The Core Formula

If a projector has a throw ratio of 1.5:1, it must be positioned 1.5 metres back to produce a 1-metre wide image. Most standard home cinema projectors have a zoom lens, meaning they have a range of throw ratios (e.g., 1.15 – 1.50). This "Zoom Ratio" (calculated as max throw / min throw) determines your placement flexibility. A larger zoom range (like 2.1x) uses more complex glass elements, which is why high-end models like the Epson TW9400 are physically larger and heavier than budget models.

2. The "F-Stop" Brightness Factor

It is a common misconception that distance reduces brightness in a vacuum (Inverse Square Law). While light spreads out, the total lumens exiting the lens remains constant. However, where you place the projector in its zoom range matters.

Wide Angle (Closest to Screen): The lens aperture is fully open (e.g., f/2.0). This allows maximum light output but may introduce slight corner softness.
Telephoto (Furthest from Screen): The aperture closes down (e.g., f/3.0) to focus the light over a longer distance. This increases contrast and sharpness but can reduce brightness by up to 25-30%. For HDR content, placing the projector closer (Wide Angle) is often preferred to maximize "nits" on screen.

Installation Geometry

3. Lens Shift vs. Keystone

4. Understanding Offset

Projectors do not shoot straight ahead; they shoot slightly upwards (if on a table) or downwards (if ceiling mounted). This is called "Offset". A 100% Offset means the bottom of the image aligns perfectly with the center of the lens. A 110% Offset means the image starts slightly above the lens level. Failing to account for offset is the #1 reason for using Keystone correction later.