Aspect Ratio refers to the ratio between the width and height of the screen.

Projection screens come in four different aspect ratios: 1:1, 4:3 and 16:9.and 16:10.

The HDTV (16:9) format is the most popular aspect ratio for home theatre, as digital television is increasingly broadcast in this format. Most DVDs currently available are HDTV (16:9) format and more and more "free to air" and cable/satellite TV will be broadcast in this format.

The Video Format (4:3) is often used for projecting analogue
TV and Video. Traditional 'data' projectors are usually 4:3
also for projection data from a computer. If HDTV or DVD is projected onto this screen, the top and bottom of the screen will not be utilised.

The Windows format (16:10) is a recently introduced format that mirrors laptops. It is the same as 16:9 with an additonal space for the start bar.

The AV Format (1:1) is sometimes used in corporate or educational situations, as this is compatible with all media, including overhead and slide projector transparencies. This format is not recommended for home use, as parts of the screen will not be used when watching dvds or television.