Throw ratio is the distance from the lens to the screen divided by the width of the image, so distance = throw ratio × image width.
Using it
A projector with a 1.5:1 ratio, throwing a 2.4-metre-wide image, needs 3.6 metres. Measure the room, decide the image width, do the multiplication, and only then look at machines whose ratio puts them somewhere you can actually mount one.
The categories it defines
Around 1.2 to 2:1 is an ordinary long-throw projector, ceiling-mounted or at the back of the room. 0.4 to 1:1 is short throw, close to the screen. Below about 0.4:1 is ultra short throw, sitting on furniture directly beneath the image.
What it does not tell you
Where the image lands vertically. That is offset, a separate figure, and a projector with a large offset placed at seat height throws its picture at the ceiling. The two specifications have to be read together.
The mistake this figure prevents
Buying on brightness and resolution, then discovering the machine has to sit 4.2 metres from a wall that is 3 metres away. Keystone correction squares that image by discarding pixels; it does not buy back the metre.
Questions people actually ask
What if the listing gives a range, like 1.2–1.6:1?
That is the zoom range. The lower number is the closest the projector can sit for a given image, the higher is the furthest. A wide zoom range is genuine placement flexibility and is worth more in a real room than most picture specifications.
Is a lower throw ratio better?
It is not better, it is different. A low ratio lets the machine sit close, which suits a small room; a higher ratio suits a projector at the back of a long room. What matters is whether the ratio matches the distance you actually have.
Last reviewed 4 September 2026