# Measuring Your Screen

=== by Bob Sutherland ===

Your computer or mobile device is broadcasting the following information about itself. Since I am not interested in knowing all about your bits and pixels I decided to set up a mirror to reflect the information back to you.

• Your physical screen size is: pixels.
• Your usable screen size is: pixels.
• The number of colours your screen can display is: bits.

## Explanation

The usable screen size is the space that is available on your screen to display my web pages and photographs. To calculate the usable screen size we start with the physical screen size and subtract the areas on your screen that your computer operating system is using for things like menus, taskbars, sidebars and scroll bars.

An answer of 1 bit of colour means that your screen is only capable of displaying black and white. This would allow it to display typing or a line art drawing.

An answer of 8 bits of colour means that your screen is capable of displaying black, white and 254 shades of grey, which is sufficient for displaying a black and white photograph.

An answer of 24 bits of colour means that your screen is capable of displaying 16,777,216 different colours, which is sufficient for displaying a colour photograph.

Your machine might be capable of displaying more than 24 bits of colour. Files sent across the Internet are usually restricted to 24 bits of colour because otherwise they become too big to upload and download.