声明：全部摘抄自网络资源，准确性和完整性不能保证，请读者自己辨别。 Introduction
一种字体（font）是一组字形（glyph）的集合，每一个字形代表了特定字样（typeface）的字符集（character set）里面的一个字符。
A font is a set of glyphs (images) representing the characters from a particular character set in a particular typeface. In professional typography the term typeface is not interchangeable with the word font, which is defined as a given alphabet and its associated characters in a single size. For example, 8-point Caslon is one font, and 10-point Caslon is another. Historically, fonts came in specific sizes determining the size of characters, and in quantities of sorts or number of each letter provided. The design of characters in a font took into account all these factors.
Measurement of font size
Point (pt, 磅)
在排版印刷中1pt是最小的测量单位， 12pt是1pica，具体是多长视情况而定。传统的排版印刷中1pt可能在0.18到0.4mm之间，这依赖于对foot的定义，现代的桌面出版中 （Desktop Publishing Point）1pt是1/72inch，也就是约0.3527mm，所以6pica是1inch。
Pixel（像素）
Inch（英寸）
millimeter（毫米）
Commonly used font size
9pt = 12px = 小五号
1pt = 4/3px
MS WORD中最大能定义1638pt大小的字体！
下表是字号与磅以及毫米之间的对应关系，并附以字样，以供大家在排版或调整布局时使用。
HTML和CSS中用的font size属性
Syntax: font-size: | | |
Possible Values:
*
o xx-small | x-small | small | medium | large | x-large | xx-large
*
o larger | smaller
*
* (in relation to parent element)
Both relative and absolute length units are supported in CSS1. Relative units give a length relative to another length property, and are preferred since they will better adjust to different media. The following relative units are available:
- em (ems, the height of the element’s font)
- ex (x-height, the height of the letter “x”)
- px (pixels, relative to the canvas resolution)
Absolute length units are highly dependent on the output medium, and so are less useful than relative units. The following absolute units are available:
- in (inches; 1in=2.54cm)
- cm (centimeters; 1cm=10mm)
- mm (millimeters)
- pt (points; 1pt=1/72in)
- pc (picas; 1pc=12pt)
要注意的是，相同大小的字体在不同的具体环境下显示出来的字体的真实大小可能不一样，差别比较小的可能是用px度量的大小。
关于x-height的定义可以看Typeface中的解释，简要的说是，对每一个字体都有一个假想的水平线叫baseline（想想小时候练习写英文字母的时候每一行都有三条或者四条横线那种作业本），x-height就是从baseline到字体最高处的高度。
Resources
- Font Size
- Point (typography)
- Typeface
- CSS改变字体大小而不影响网页
- 【知识】字体中“号”“磅”及“毫米”的关系
- Length Units
Technorati : CSS, HTML, Web Browser
Del.icio.us : CSS, HTML, Web Browser
Ice Rocket : CSS, HTML, Web Browser
Flickr : CSS, HTML, Web Browser
Zooomr : CSS, HTML, Web Browser
Buzznet : CSS, HTML, Web Browser
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