Projector Throw Distance Calculator
Throw distance for a given screen size and projector throw ratio — or the screen width you get at a set distance — with short-throw and ultra-short-throw ranges, aspect ratio and lens shift notes.
How it works
Throw distance = throw ratio × image width; width = diagonal ÷ √(1 + 1/AR²); 16:9 width = 0.872 × diagonal
A projector’s lens is described by its throw ratio — how far away it must sit for each unit of image width. A ratio of 1.5 means a 2 m wide picture needs the lens 3 m from the wall; zoom lenses give a range. Short-throw lenses (under 1.0) let a projector sit on a coffee table, ultra-short-throw units (0.2–0.4) sit inches from the wall, and long-throw lenses suit halls and cinemas. Because screens are sold by diagonal, the calculator converts through the aspect ratio first. Remember that the specification measures from the lens to the screen, that lens shift and keystone affect placement but not the throw, and that brightness falls as the image grows — a 120-inch image needs roughly 1.4 times the lumens of a 100-inch one.
Worked example
A 120″ 16:9 screen is 2.66 m wide; a 1.5–2.13 zoom lens places the projector between 4.0 and 5.7 m away.
Frequently asked questions
What throw ratio do I need for a small room?
Divide your available distance by the screen width you want. 3 m for a 2.2 m wide screen is a ratio of 1.36 — a standard lens; 1.5 m would need a short throw of 0.68.
Does 4K change anything?
Not the geometry. It does justify sitting closer — about 1.0–1.2× the screen width instead of 1.5–2× for HD.
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This calculator is for educational purposes. Double-check important results before acting on them.