Throw Ratio and Throw Distance Explained

Every projector placement starts with one number: the throw ratio. It tells you how far the projector must be from the surface to create an image of a given width.

The formula

throw ratio = throw distance ÷ image width

So:

throw distance = throw ratio × image width
image width = throw distance ÷ throw ratio

A projector with a 1.5:1 lens produces a 10 m wide image from 15 m away. Move it to 30 m and the image grows to 20 m wide (and four times dimmer, because the same light covers four times the area).

Image height follows from the aspect ratio: a 16:10 (WUXGA) image 10 m wide is 6.25 m tall; a 16:9 image is 5.63 m tall.

Try it with the throw-distance calculator — or open any model in the projector database, where we pre-compute throw tables for the standard lens and every optional lens.

Zoom lenses give a range

Most lenses are zooms, quoted as a range like 1.39–2.23:1. At the short end the image is largest for a given distance; at the long end it is smallest. If your required throw ratio falls inside the range, the lens works. Many installation lenses lose some brightness at the telephoto end.

Lens categories

Category	Typical throw ratio	Use
Ultra-short throw	< 0.4:1	Projector right next to the surface
Short throw	0.4 – 1.0:1	Tight streets, object mapping, immersive rooms
Standard zoom	1.2 – 2.5:1	Most indoor and medium outdoor setups
Long throw	2.5 – 8:1	Projecting across squares, rivers, stadiums

Lens shift instead of tilt

If the projector is lower or higher than the centre of the surface, use lens shift rather than tilting the projector and correcting with keystone. Shift moves the image optically without losing pixels. Large-venue projectors often offer ±50% or more vertical shift; check the spec before you choose a position.

Projecting at an angle

When you cannot stand straight in front of the facade, the image becomes a trapezoid. Small angles are corrected in the mapping software with corner-pin or mesh warp. At steep angles, pixels on the far side are stretched and dimmer — split the surface between two projectors from different sides instead.

A practical example

You want to cover a facade 24 m wide. The only position is a rooftop 40 m away.

1. Required throw ratio = 40 ÷ 24 = 1.67:1.
2. With a single WUXGA projector the image is 24 × 15 m — check that one projector is bright enough with the brightness calculator.
3. If you need two projectors blended side by side with a 15% overlap, each image must be about 13 m wide (2 × 13 m − 15% of 13 m ≈ 24 m): throw ratio = 40 ÷ 13 ≈ 3.1:1 — now you need a longer lens.

FAQ

What throw ratio do I need?

Divide the distance available by the width of the image you want. Choose a lens whose zoom range includes that number, with some margin on both sides.

Is a short-throw lens always better?

No. Short-throw lenses let you get close, but projectors close to the surface create sharper shadows when people walk in front, and wide-angle lenses can show more distortion at the edges.

Does throw distance affect brightness?

The projector emits the same lumens, but a larger image spreads them over more area, so the surface gets darker. Moving the projector twice as far away makes the image four times dimmer.