This translation is incomplete. Please help translate this article from English.

The font-weight CSS propery specifies the weight (or boldness) of the font. The font weights available to you will depend on the font-family you are using. Some fonts are only available in normal and bold.

Syntax

/* Keyword values */
font-weight: normal;
font-weight: bold;

/* Keyword values relative to the parent */
font-weight: lighter;
font-weight: bolder;

/* Numeric keyword values */
font-weight: 1
font-weight: 100;
font-weight: 100.6;
font-weight: 123;
font-weight: 200;
font-weight: 300;
font-weight: 321;
font-weight: 400;
font-weight: 500;
font-weight: 600;
font-weight: 700;
font-weight: 800;
font-weight: 900;
font-weight: 1000;

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

The font-weight property is specified using any one of the values listed below.

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 heavier than the parent element (among the available weights of the font).
<number>
A <number> value between 1 and 1000, inclusive. Higher numbers represent weights that are bolder than (or as bold as) lower numbers. Certain commonly used values correspond to common weight names, as described in the Common weight name mapping section below.

In earlier versions of the font-weight specification, the property accepts only keyword values and the numeric values 100, 200, 300, 400, 500, 600, 700, 800, and 900. CSS Fonts Level 4 extends the syntax to accept any number between 1 and 1000. This enables variable fonts to provide a much finer-grained range of font weights. Note that this is not yet supported by all browsers.

Fallback weights

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

  • If the target weight given is between 400 and 500 inclusive:
    • Look for available weights between the target and 500, in ascending order.
    • If no match is found, look for available weights less than the target, in descending order.
    • If no match is found, look for available weights greater than 500, in ascending order.
  • If a weight less than 400 is given, look for available weights less than the target, in descending order. If no match is found, look for available weights greater than the target, in ascending order.
  • If a weight greater than 500 is given, look for available weights greater than the target, in ascending order. If no match is found, look for available weights less than the target, in descending order.

Meaning of relative weights

When lighter or bolder is specified, the following chart shows how the absolute font weight of the element is determined:

Inherited value bolder lighter
100 400 100
200 400 100
300 400 100
400 700 100
500 700 100
600 900 400
700 900 400
800 900 700
900 900 700

Common weight name mapping

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

Value Common weight name
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)

Variable fonts

Most fonts have a particular weight which corresponds to one of the numbers in Common weight name mapping. However some fonts, called variable fonts, can support a range of weights with a more or less fine granularity, and this can give the designer a much closer degree of control over the chosen weight.

For TrueType or OpenType variable fonts, the "wght" variation is used to implement varying widths.

For the example below to work, you'll need a browser that supports the CSS Fonts Level 4 syntax in which font-weight can be any number between 1 and 1000.

HTML

<header>
    <input type="range" id="weight" name="weight" min="1" max="1000" />
    <label for="weight">Weight</label>
</header>
<div class="container">
    <p class="sample">...it would not be wonderful to meet a Megalosaurus, forty feet long or so, waddling like an elephantine lizard up Holborn Hill.</p>
</div>

CSS

/*
Mutator Sans is created by LettError (https://github.com/LettError/mutatorSans)
and is used here under the terms of its license:
https://github.com/LettError/mutatorSans/blob/master/LICENSE
*/

@font-face {
  src: url('https://mdn.mozillademos.org/files/16011/MutatorSans.ttf');
  font-family:'MutatorSans';
  font-style: normal;
}

label {
  font: 1rem monospace;
  white-space: nowrap;
}

.container {
  max-height: 150px;
  overflow-y: auto;
}

.sample {
  text-transform: uppercase;
  font: 1.5rem 'MutatorSans', sans-serif;
}

JavaScript

let weightLabel = document.querySelector('label[for="weight"]');
let weightInput = document.querySelector('#weight');
let sampleText = document.querySelector('.sample');

function update() {
  weightLabel.textContent = `font-weight: ${weightInput.value};`;
  sampleText.style.fontWeight = weightInput.value;
}

weightInput.addEventListener('input', update);

update();

Formal syntax

<font-weight-absolute> | bolder | lighter

where
<font-weight-absolute> = normal | bold | <number>

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 heavier than
   normal but less than a standard bold. */
div {
 font-weight: 600;
}

/* Set span text to be one step lighter
   than its parent. */
span {
  font-weight: lighter;
}

Result

Accessibility concerns

People experiencing low vision conditions may have difficulty reading text set with a font-weight value of 100 (Thin/Hairline) or 200 (Extra Light), especially if the font has a low contrast color ratio.

Specifications

Specification Status Comment
CSS Fonts Module Level 4
The definition of 'font-weight' in that specification.
Working Draft Defines font-weight to accept any numbers between 1 and 1000.
.CSS Fonts Module Level 3
The definition of 'font-weight' in that specification.
Candidate Recommendation No change.
CSS Transitions
The definition of 'font-weight' in that specification.
Working Draft Defines font-weight as animatable.
CSS Level 2 (Revision 1)
The definition of 'font-weight' in that specification.
Recommendation No change.
CSS Level 1
The definition of 'font-weight' in that specification.
Recommendation Initial definition.

Initial valuenormal
Applies toall elements. It also applies to ::first-letter and ::first-line.
Inheritedyes
Mediavisual
Computed valuethe keyword or the numerical value as specified, with bolder and lighter transformed to the real value
Animation typea font weight
Canonical orderthe unique non-ambiguous order defined by the formal grammar

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support212133.51.3
<number> syntax62 ?61 No ? ?
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support1 Yes Yes463.1 Yes
<number> syntax ?62 ?61 ? ? ?

Document Tags and Contributors

Contributors to this page: fabio.rahamim
Last updated by: fabio.rahamim,