Technical Tips - Screen size and resolution

This is not really a Technical Tip, more the result of some detailed research, but this section seemed the best place to publish it. The research started when I was asked the apparently simple question - "This laptop has two alternative screen resolutions. Which should I buy?". But getting to the answer was far more complicated than I could ever have thought.

Beating the jargon

  • Aspect ratio : The ratio of the width:height of the screen. 5:4 and 4:3 are considered "normal", 16:10 is generally referred to as "widescreen". The vast majority of computer screens are one of these three aspect ratios.
  • Display (or screen) resolution : The number of displayed pixels in each dimension, generally as width x height, e.g. 1024x768, 1280x800, 1280x1024.
  • Native resolution : A single fixed display resolution, generally the maximum that can be displayed on a TFT "flat panel" screen. TFT screens, unlike the older cathode ray tube (CRT) screens, cannot be rescaled without a noticeable loss of quality.
  • Pixel (or dot) pitch : The pixel is the smallest item of information in an image. The pixel pitch is the distance between pixels (dots) of the same colour on the screen. A closer spacing produces a sharper image. This information is rarely provided in the technical specifications for portable computers (laptops and netbooks) but can be calculated using the Display Dimensions Calculator website below:
  • Dot pitch explained on Wikipedia
  • Display Dimensions Calculator
  • Screen size : Normally measured across the diagonal of the screen and expressed in inches, often rounded up or down. Netbooks are generally 10" or 12"; Notebooks (or laptops) are generally 13", 14", 15" or 17"; Monitors for desktop computers are generally 17" and larger.

Why is all this important?

  • For any given screen size, screens with a higher native resolution (shorter pixel pitch) will make screen items look smaller than "normal", screens with a lower native resolution (longer pixel pitch) will make screen items look larger than "normal".
  • There has been a recent (2008-10) trend for laptops to be supplied with screens at higher native resolutions, for a given screen size, than would have been considered normal just a few years ago.
  • The TFT "flat panel" screens now in almost universal use for both desktop and laptop computers should always be used at their native resolution for the sharpest display. Decreasing the resolution, to increase the displayed size of text and images, will always cause some blurring.
  • It is therefore extremely important that screen size and resolution are considered together when determining what is likely to provide the most comfortable viewing experience for an individual user. In particular it should not be assumed that a higher screen resolution is always "better" - in some cases a high screen resolution on a small screen can make text difficult to read and images uncomfortably small to look at.

What is "normal"?

  • Windows XP and Vista have a normal display setting of 96 dots-per-inch (dpi), equivalent to a pixel pitch of approximately 0.262mm.
  • In practice a degree of variation between 110dpi (0.230mm) and 90dpi (0.280mm) will be acceptable to most users.
  • Some users will consider the display to be "too small" on a screen above 110dpi (below 0.230mm). This is typical for many current 13" and 14" notebooks.
  • Some users will consider the display to be "too large" on a screen below 90dpi (above 0.280mm). This is typical for some of the cheaper flat screen monitors.
  • Examples of commonly-available screen sizes/ resolutions/ pixel pitches:
  • 10" screen at 1024x600 - 118dpi/0.214mm (typical netbook).
  • 12.1" screen at 1280x800 - 125dpi/0.204mm (typical ultra-portable).
  • 13.3" screen at 1280x800 - 113dpi/0.224mm (typical notebook).
  • 14.1" screen at 1280x800 - 107dpi/0.237mm (typical notebook).
  • 15.4" screen at 1280x800 - 98dpi/0.259mm (typical notebook).
  • 17" screen at 1440x900 - 96dpi/0.254mm (typical notebook).
  • 17" screen at 1280x1024 - 96dpi/0.263mm (typical desktop monitor).
  • 20.1" screen at 1600x1200 - 99dpi/0.255mm (typical desktop monitor).
  • 20.1" screen at 1680x1050 - 98dpi/0.258mm (typical desktop monitor).
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