font-weight

Summary

The font-weight CSS property specifies the weight or boldness of the font. Some fonts are only available in normal and bold.

Syntax

font-weight: normal;
font-weight: bold;

/* Relative to the parent */
font-weight: lighter;
font-weight: bolder;

font-weight: 100;
font-weight: 200;
font-weight: 300;
font-weight: 400;
font-weight: 500;
font-weight: 600;
font-weight: 700;
font-weight: 800;
font-weight: 900;

/* Global values */
font-weight: inherit;
font-weight: initial;
font-weight: unset;

Values

normal

Normal font weight. Same as 400.

bold

Bold font weight. Same as 700.

lighter

One font weight lighter than the parent element (among the available weights of the font).

bolder

One font weight darker than the parent element (among the available weights of the font).

100, 200, 300, 400, 500, 600, 700, 800, 900

Numeric font weights for fonts that provide more than just normal and bold.

Fallback

If the exact weight given is unavailable, then the following heuristic is used to determine the weight actually rendered:

• If a weight greater than 500 is given, the closest available darker weight is used (or, if there is none, the closest available lighter weight).
• If a weight less than 400 is given, the closest available lighter weight is used (or, if there is none, the closest available darker weight).
• If a weight of exactly 400 is given, then 500 is used. If 500 is not available, then the heuristic for font weights less than 400 is used.
• If a weight of exactly 500 is given, then 400 is used. If 400 is not available, then the heuristic for font weights less than 400 is used.

This means that for fonts that provide only normal and bold, 100-500 are normal, and 600-900 are bold.

Meaning of relative weights

When lighter or bolder is given, the following chart is used to calculate the absolute weight of the element:

Common weight name mapping

The 100 to 900 values roughly correspond to the following common weight names:

100

Thin (Hairline)

200

Extra Light (Ultra Light)

300

Light

400

Normal

500

Medium

600

Semi Bold (Demi Bold)

700

Bold

800

Extra Bold (Ultra Bold)

900

Black (Heavy)

Interpolation

A font-weight value is interpolated via discrete steps (multiples of 100). The interpolation happens in real number space and is converted to an integer by rounding to the nearest multiple of 100, with values halfway between multiples of 100 rounded towards positive infinity.

Formal syntax

normal | bold | bolder | lighter | 100 | 200 | 300 | 400 | 500 | 600 | 700 | 800 | 900

Examples

HTML

<p>
  Alice was beginning to get very tired of sitting by her sister on the
  bank, and of having nothing to do: once or twice she had peeped into the
  book her sister was reading, but it had no pictures or conversations in
  it, 'and what is the use of a book,' thought Alice 'without pictures or
  conversations?'
</p>

<div>I'm heavy<br/>
  <span>I'm lighter</span>
</div>

CSS

/* Set paragraph text to be bold. */
p {
  font-weight: bold;
}

/* Set div text to two steps darker than
   normal but less than a standard bold. */
div {
 font-weight: 600;
}

/* Sets text enclosed within span tag 
   to be one step lighter than the parent. */
span {
  font-weight: lighter;
}

Result

Specifications

Browser compatibility