The number of pixels can only tell you the printed size if you also take in to account DPI, which is 'the number of pixels to print per inch'.
Originally Posted by 1Being1
So 1024 x 768 at '300 DPI' (300 pixels per inch) comes out at around 3 inches by 2 inches (1024 split in to chunks of 300 per inch), but if you use the default DPI of 72 you get way more inches because you have 1024 pixels split in to chunks of 72 per inch.
If you're typing size in to the box and you want to print at a certain size, don't use pixels, use the Inches option and type the number of inches you want, and the DPI you will be printing at. That way the number of pixels is calculated for you and you don't need to worry about it.