Pixels to Ems Conversion Table for CSS

A companion reference to the article, The Incredible Em and Elastic Layouts With CSS.

The em values in the table assume that the generic browser default setting of 16px font size has not being changed. It also assumes that the <body> has font size set to 1em or 100%.

px font-size	em equivalent	* Rounded to 3dp	1px in ems	Notes
11	0.689	*	0.091
12	0.750		0.083
13	0.814	*	0.077
14	0.875		0.071
15	0.938	*	0.067
16	1.000		0.063	Browser standard default
17	1.064	*	0.059
18	1.125		0.056
19	1.188	*	0.053
20	1.250		0.050
21	1.313	*	0.048
22	1.375		0.046
23	1.438	*	0.044
24	1.500		0.042
25	1.563	*	0.040
26	1.625		0.039
27	1.688	*	0.037
28	1.750		0.036
29	1.813	*	0.035
30	1.875		0.033

Formula to calculate em equivalent for any pixel value required

1 ÷ parent font size (px) × required pixels = em equivalent

Example: 770px wide, centred elastic layout using CSS and ems

N.B. This assumes the browser default font size is unchanged at 16px. body{} selector set to font-size:1em;. Using the forumla*:

1 ÷ 16 × 770 = 48.125em

CSS:

body{
font-size:1em;
text-align:center;
}

div{
width:48.125em;
margin;0 auto;
}

HTML:

<html>
<body>

<div>
…
</div>

</body>
</html>

*I deliberately hooked the formula for the tutorial around 1px, as a value that designers can easily relate to. However, there is a faster way of calculating an em value that I use. You need to be familliar with the sticky issue of CSS inheritance and know the font size of the parent, but it goes like this:

Required element pixel value ÷ parent font size in pixels = em value

So, our required width of 770px in ems can be calculated like this:

770 ÷ 16 = 48.125em

Jon Tangerine / silo / CSS / Pixels to Ems Conversion Table for CSS

Formula to calculate em equivalent for any pixel value required

Example: 770px wide, centred elastic layout using CSS and ems

CSS:

HTML:

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