Projector aspect ratio is the width-to-height ratio of the displayed image, measured in inches. Some projectors can support multiple aspect ratios.
The most common aspect ratios for projectors are 4:3, 5:4, and 16:9. That means that the chip (or panel) inside the projector is shaped in the specified 4:3, 5:4 or 16:9 proportions. The chip is like a miniature version of the image you will see on your screen.
Currently the most common aspect ratio in projectors is 4:3, which is the same as most televisions and computer monitors.
16:9 — BEST for wide-screen images, as it is one-third wider than standard displays. This aspect ratio gives viewers the full picture of movies and broadcasts. It is the format for HDTV video and some SDTV video.
5:4 — This is the display aspect ratio for images with SXGA resolution. Wide-screen images will appear cropped at this ratio.
4:3 — The standard display aspect ratio for TV, as well as for images with VGA, SVGA, XGA, or UXGA resolution. Wide-screen images will appear cropped at this ratio.