What is throw ratio and how do I calculate the lens I need?
Lenses, Throw Ratios, & Projection Surfaces
Throw ratio is the relationship between the projector's distance from the screen (throw distance) and the width of the image it produces. The formula is: Throw Ratio = Throw Distance ÷ Screen Width. So if your projector is 30 feet from a 15-foot-wide screen, your throw ratio is 2.0.
To figure out which lens you need, use the formula: Lens Ratio × Screen Width = Projection Distance. You can also rearrange it: divide Projection Distance by Screen Width to find the ratio you need, or divide Projection Distance by Lens Ratio to find the maximum screen width you can achieve from a given position.
One important note: lens ratio specifications aren't standardized across manufacturers. Barco bases its lens ratios on the projector's resolution format (SD, HD, WUXGA, 4K), while Epson bases theirs on chip size. Always verify against the specific projector model you're using.
Read more about projectors in our Comprehensive Guide to Projectors article.