font-weight

The font-weight descriptor takes one of the following forms:

• The keyword auto.
• A single <font-weight-absolute> value.
• A pair of <font-weight-absolute> values, separated by a space.

Each <font-weight-absolute> may be any one of the following:

normal

Normal font weight. Same as 400.

bold

Bold font weight. Same as 700.

<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.

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

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 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 weights.

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

font-weight = 
  auto                         |
  <font-weight-absolute>{1,2}  

<font-weight-absolute> = 
  normal             |
  bold               |
  <number [1,1000]>  

In this example we include two fonts, one normal weight, one bold weight, from the "Fira Sans" font family using two @font-face at rules. We set font-weight descriptors to match the weight of the fonts.

After this, CSS rules can select the normal or the bold font for the "Fira Sans" family just by setting the font-weight property. Note that the <strong> HTML element also selects the bold font, because by default <strong> elements have a CSS font-weight property value of bold.

HTML

<p class="one">Fira Sans, `normal` weight paragraph</p>
<p class="two">Fira Sans, `bold` weight paragraph</p>
<p><strong>Fira Sans, &lt;strong&gt; element (`bold`)</strong></p>

CSS

@font-face {
  font-family: "Fira Sans";
  font-weight: normal;
  src: url("https://mdn.github.io/shared-assets/fonts/FiraSans-Regular.woff2");
}

@font-face {
  font-family: "Fira Sans";
  font-weight: bold;
  src: url("https://mdn.github.io/shared-assets/fonts/FiraSans-Bold.woff2");
}

body {
  font-family: "Fira Sans", serif;
  font-size: 2rem;
}

p.one {
  font-weight: normal;
}

p.two {
  font-weight: bold;
}

Result

This example demonstrates how authors can include multiple fonts for multiple font-weights (and font-styles), by including multiple @font-face declarations with the same font-family value. By setting the font-weight descriptors using ranges from 1 to 1000, in the rest of your stylesheets, you can declare a font-weight (or font-style), and know the appropriate font will be used.

HTML

<p class="one">This has a font weight of 100</p>
<p class="three">This has a font weight of 300</p>
<p class="four">This has a font weight of 400</p>
<p class="five">This has a font weight of 500</p>
<p class="seven">This has a font weight of 700</p>
<p class="nine">This has a font weight of 900</p>

CSS

We include four @font-face declarations for four different fonts from the FireSans font family, as seen in the previous example. Each declaration is set to a different range of font-weight values, but all use the same font name.

The first declaration uses FiraSans-Regular and its associated font-weight range includes the entire possible range of font weight values.

The other three declarations use the light, bold, and extra-bold versions of the font, and their associated font-weight ranges define subsets of the range as follows:

• the light font is associated with the range 1-300
• the bold font is associated with the range 500-700
• the extra-bold font is associated with the range 700-1000

The CSS cascade ensures that the three latter declarations override parts of the the range that was set in the FiraSans-Regular declaration.

@font-face {
  font-family: "Fira Sans";
  font-weight: 1 1000;
  src: url("https://mdn.github.io/shared-assets/fonts/FiraSans-Regular.woff2");
}

@font-face {
  font-family: "Fira Sans";
  font-weight: 1 300;
  src: url("https://mdn.github.io/shared-assets/fonts/FiraSans-Light.woff2");
}

@font-face {
  font-family: "Fira Sans";
  font-weight: 500 700;
  src: url("https://mdn.github.io/shared-assets/fonts/FiraSans-Bold.woff2");
}

@font-face {
  font-family: "Fira Sans";
  font-weight: 700 1000;
  src: url("https://mdn.github.io/shared-assets/fonts/FiraSans-ExtraBold.woff2");
}

body {
  font-family: "Fira Sans", serif;
  font-size: 2rem;
}

p.one {
  font-weight: 100;
}

p.three {
  font-weight: 300;
}

p.four {
  font-weight: 400;
}

p.five {
  font-weight: 500;
}

p.seven {
  font-weight: 700;
}

p.nine {
  font-weight: 900;
}

Result

The seven paragraph uses the extra bold font. While font-weight: 700 matches both the FiraSans-Bold and FiraSans-ExtraBold declarations, as the FiraSans-ExtraBold is declared later, it overrides the FiraSans-Bold for that value.

Similarly, the 100 and 300 both use the light font; although FiraSans-Regular and FiraSans-Light both include 300 in their ranges, FiraSans-Light is declared later. Alternatively, we could have declared FiraSans-Regular after FiraSans-Light, but we would need to change the font-weight descriptor range if we do so.

In this example we're using the font-weight descriptor to restrict the range of weights that can be set when using a variable font.

We include a variable font, "League Mono", using a single @font-face at-rule. We use a font-weight: 300 700 value to effectively limit the range of weights that are available. If a CSS rule uses our "League Mono" font, then if it specifies a weight outside this range the weight it gets is clamped to the range.

HTML

We include a paragraph with <output> initially set to 400, as that is the the default font-weight for unstyled paragraph text. This paragraph is nestled between two other paragraphs, so you can compare rendered versus declared font weight values.

We include an <input/range> of type range, nested in a <label>, setting the step to 50.

<p>LeagueMono, font-weight: 300 (comparison)</p>
<p id="example">LeagueMono, font-weight: <output>400</output> (example)</p>
<p>LeagueMono, font-weight: 700 (comparison)</p>
<label
  >Change the font size:
  <input type="range" min="50" max="1000" step="50" value="400" />
</label>

CSS

We set the font-weight descriptor range to 300 700, clamping the variable font to that range.

@font-face {
  font-family: LeagueMono;
  src: url("https://mdn.github.io/shared-assets/fonts/LeagueMono-VF.ttf");
  font-weight: 300 700;
}

p {
  font-family: LeagueMono, serif;
  font-size: 1.5rem;
}

p:first-of-type {
  font-weight: 300;
}

p:last-of-type {
  font-weight: 700;
}

JavaScript

We include an event handler that updates the paragraph's font-weight property value, and updates the text to reflect the change:

const text = document.querySelector("#example");
const log = document.querySelector("output");
const range = document.querySelector("input");

range.addEventListener("change", () => {
  text.style.fontWeight = range.value;
  log.innerText = range.value;
});

Result

Change the font weight of the paragraph via the range. Note that the example paragraph does not get lighter than the 300 paragraph above it or bolder than the 700 paragraph below it; the font weight is clamped to the range defined by the font-weight descriptor.

• font-display
• font-family
• font-stretch
• font-style
• font-feature-settings
• font-variation-settings
• src
• unicode-range descriptor