font-weight

The font-weight CSS property 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:

Common weight name mapping

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

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.

• MDN Understanding WCAG, Guideline 1.4 explanations
• Understanding Success Criterion 1.4.8 | W3C Understanding WCAG 2.0

Specifications

Browser compatibilityUpdate compatibility data on GitHub