TR (Throw Ratio)

Throw ratio is the relationship between a projector’s throw distance (the distance from the lens to the screen) and the screen width. It is expressed as a dimensionless ratio.

Throw Ratio = Throw Distance / Screen Width

Examples

If a projector is placed 4.5 m from a 3.0 m wide screen:

TR = 4.5 / 3.0 = 1.5

This lens has a throw ratio of 1.5:1 (or simply 1.5).

Solving for Any Variable

Unknown	Formula
Throw distance	Distance = TR × Screen Width
Screen width	Width = Distance ÷ TR
Throw ratio	TR = Distance ÷ Width

Use the SANE Throw Ratio Calculator to solve interactively.

Zoom Lenses

Zoom lenses specify a range of throw ratios, e.g. 1.2–1.8. The minimum ratio produces the largest image at a given distance; the maximum ratio produces the smallest.

Typical Throw Ratio Ranges

Lens Category	Typical Range
Ultra-short throw (UST)	0.1 – 0.4
Short throw	0.4 – 1.0
Standard	1.0 – 2.5
Long throw	2.5 – 8.0+

Notes for Installation

• Always verify the exact throw ratio from the manufacturer’s specification sheet for the lens you are using. Published values are nominal; actual image size may vary slightly.
• Account for lens shift range if the projector will not be centered on the screen axis.
• For screens taller than wide (portrait), the throw ratio formula still uses screen width.