The aspect ratio of an element describes the proportional relationship between its width and its height.

It is commonly expressed as two numbers separated by a colon, as in 16:9. For an x:y aspect ratio, no matter how big or small the element is, if the width is divided into x units of equal length and the height is measured using this same length unit, the height will be measured to be y units.

For example, older square box tv's are typically 4:3 aspect ratio (or 1:1.33). This translates to meaning basically, for every 4 pixels across, 3 pixels are down. We can extrapolate from that, a standard-definition tv screen is commonly 640 x 480 pixels.

• 4:3 is used for many computer monitors and older, non-widescreen televisions.
• 1:1 is an uncommon square-format aspect ratio occasionally used in photography.
• 5:4 is a computer monitor resolution, now more commonly used in mobile telephone cameras.
• 16:9 is the aspect ratio used for High Definition television, as well as movies.
• 14:9 is a compromise aspect ratio used to create a picture acceptable to both 4:3 and 16:9 televisions.
• 16:10 is utilized in the majority of widescreen computer monitors.

16:9 aspect ratio

The main advantage of a 16:9 aspect ratio is that it is the standard that High Definition content is output at. This makes it vital if you plan on watching High Definition movies or sports, especially as these are now becoming increasingly more available. This is primarily due to the declining cost and growing popularity of Blu-Ray players, as well as the fact that many governments are actively encouraging television companies to make HDTV broadcasts available. The 16:9 aspect ratio is particularly appropriate if you watch many modern films on a home movie theatre since most movies are now produced in 16:9 format.

4:3 aspect ratio

While the 4:3 aspect ratio is viewed as somewhat dated, it is still very common and is still the standard aspect ratio for computer screens. While it is true that High Definition content is becoming more and more prevalent, the majority of broadcasters still output in a 4:3 aspect ratio. While the same cannot be said for films, if you still watch a lot of VHS tapes of older films then a 4:3 television will allow for the image to take up the screen. Displayed on a 16:9 television it would appear stretched, or would have black borders running along the edges.

Common Device Aspect Ratios

| 4:3    |   3:2       |    16:10        |     17:10    |    16:9   |
| iPad 1 | iPhone 3GS- | Windows Phone 7 | Galaxy Tab 7 | Nokia C7  |
| iPad 2 | iPhone 4    | Google Nexus    |              | MeeGo N9  |
| iPad 3 | iPhone 4S   | Galaxy 10.1     |              | iPhone 5  |
| iPad 3 |             | Motorola Xoom   |              |           |
|        |             |                 |              |           |