pixel size 72dpi 96dpi

Hypertext Markup Language - 2.0 No definition of pixel

HTML 3.2 Reference Specification added tables. in tables and inline images, pixel values for width and height refer to screen pixels.

HTML 4.01 Specification, Basic HTML data types Pixels: The value (%Pixels; in the DTD) is an integer that represents the number of pixels of the canvas (screen, paper)

Cascading Style Sheets, level 1 Pixel units, as used in the last rule, are relative to the resolution of the canvas, i.e. most often a computer display. If the pixel density of the output device is very different from that of a typical computer display, the UA should rescale pixel values. The suggested reference pixel is the visual angle of one pixel on a device with a pixel density of 90dpi and a distance from the reader of an arm's length. For a nominal arm's length of 28 inches, the visual angle is about 0.0227 degrees.

Cascading Style Sheets, level 2 revision 1, CSS 2.1 Specification, Syntax and basic data types
Pixel units are relative to the resolution of the viewing device, i.e., most often a computer display. If the pixel density of the output device is very different from that of a typical computer display, the user agent should rescale pixel values. It is recommended that the reference pixel be the visual angle of one pixel on a device with a pixel density of 96dpi and a distance from the reader of an arm's length. For a nominal arm's length of 28 inches, the visual angle is therefore about 0.0213 degrees.
For reading at arm's length, 1px thus corresponds to about 0.26 mm (1/96 inch). When printed on a laser printer, meant for reading at a little less than arm's length (55 cm, 21 inches), 1px is about 0.20 mm. On a 300 dots-per-inch (dpi) printer, that may be rounded up to 3 dots (0.25 mm); on a 600 dpi printer, it can be rounded to 5 dots.

pt, point; 1pt is equal to 1/72 inch.
pc, picas; 1 pica is equal to 12 points.

CSS3 Values and Units The pixel unit, 'px' is relative to the resolution of the viewing device. For example, the viewing device can be a computer display or a printer. Normally, the pixel unit refers to physical pixels of the viewing device. However, if the pixel density of the output device is very different from that of a typical computer display, the user agent should rescale pixel values. It is recommended that the reference pixel be the visual angle of one pixel on a device with a pixel density of 96dpi and a distance from the reader of an arm's length. For a nominal arm's length of 28 inches, the visual angle is therefore about 0.0213 degrees.

For reading at arm's length, 1px thus corresponds to about 0.26mm (1/96 inch). When printed on a laser printer, meant for reading at a little less than arm's length (55 cm, 21 inches), 1px is about 0.21mm. On a 300 dots-per-inch (dpi) printer, that may be rounded up to 3 dots (0.25 mm); on a 600 dpi printer, it can be rounded to 5 dots.

Say No to 72 dpi display resolution history Apple 72 dpi, Windows 96 dpi 120 dpi, Unix X11 75 dpi fonts 100 dpi font