CSS font-size Property

The font-size property defines the font size of the text.

Font size can be defined by the following ways:

absolute-size
relative-size
length
percentage

Absolute font size includes the following values:

xx-small
x-small
small
small
x-large
xx-large

Relative font size includes the following values:

smaller
larger

Lengths can be relative lengths (em, ex, px) and absolute lengths (in, cm, mm, pt, pc). Percentages specify an absolute font size relative to the font size of the parent element.

Initial Value	medium
Applies to	All elements. It also applies to ::first-letter and ::first-line.
Inherited	Yes.
Animatable	Yes.
Version	CSS1
DOM Syntax	object.style.fontSize = "15px";

Syntax

font-size: medium | xx-small | x-small | small | large | x-large | xx-large | smaller | larger | length | initial | inherit;

Example of the font-size property:

<!DOCTYPE html>
<html>
  <head>
    <title>Title of the document</title>
    <style>
      h1 {
        font-size: 24pt;
      }
      h3 {
        font-size: 26px;
      }
      p {
        font-size: 1em;
      }
      a {
        font-size: 100%;
      }
      span {
        font-size: x-small;
      }
    </style>
  </head>
  <body>
    <span>This span is written with x-small value.</span>
    <p>This paragraph is written with 1em font-size.</p>
    <a href="https://www.w3docs.com/">This hyperlink is written with 100% font-size.</a>
    <h3>We used x-small font size for this heading.</h3>
    <h1>We set the font size 24pt  for this heading.</h1>
  </body>
</html>

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Result

Usage of percentage values

Percentage values are relative to the font-size of the parent element. The code below shows its usage:

Example of the font-size property specified in percentage:

<!DOCTYPE html>
<html>
  <head>
    <title>Title of the document</title>
    <style>
      h3 {
        font-size: 125%;
      }
    </style>
  </head>
  <body>
    <h3>We used x-small font size for this heading.</h3>
    <span>This span is written with x-small value.</span>
    <p>This paragraph is written with 1em font-size.</p>
  </body>
</html>

Usage of the em unit

The em unit is considered to be a relative unit. It is based on the calculated value of its parent element’s font size. In the code below, the paragraph will be 32px, because 2x16=32, and the heading will have a font-size of 48px because 3x16=48px. This method is very useful because we can be sure that all the child elements will always be relative to each other.

Example of the font-size property with the "em" value:

<!DOCTYPE html>
<html>
  <head>
    <title>Title of the document</title>
    <style>
      .container {
        font-size: 16px;
      }
      p {
        font-size: 2em;
      }
      h2 {
        font-size: 3em;
      }
    </style>
  </head>
  <body>
    <div class="container">
      <h2>Here is the heading</h2>
      <p>Here is the text.</p>
    </div>
  </body>
</html>

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Usage of the rem unit

In the case of using the rem unit, the font-size depends on the value of the HTML element. In the example below, the rem unit is inherited from the HTML element, that’s why it is equal to 24px. So, the heading will have a font-size of 24px, because 1.5x16=24px.

Example of the font-size property with the "rem" value:

<!DOCTYPE html>
<html>
  <head>
    <title>Title of the document</title>
    <style>
      html {
        font-size: 16px;
      }
      h2 {
        font-size: 1.5rem;
      }
    </style>
  </head>
  <body>
    <div class="container">
      <h2>Here is the heading</h2>
      <p>Here is the text.</p>
    </div>
  </body>
</html>

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Usage of the ex unit

In the case of the ex unit, 1ex is equal to the calculated height of the HTML element’s letter x. In the code example below, the HTML element is 15px. The x-height of that particular font will determine all the other font-sizes.

.exunit {
  font-size: 15ex;
}

Usage of viewport units

Viewport units (vw and vh) are used for setting the font-size of an element, which is relative to the size of the viewport.

1vw = 1% of viewport width
1vh = 1% of viewport height

.viewport {
  font-size: 120vh;
}

Example of the font-size property with the "length" value:

<!DOCTYPE html>
<html>
  <head>
    <title>Title of the document</title>
    <style>
      span {
        color: green;
        font-size: 2vh;
      }
      p {
        color: red;
        font-size: 1em;
      }
      .length {
        color: orange;
        font-size: 30px;
      }
      h3 {
        color: lightblue;
        font-size: 3ex;
      }
      h1 {
        color: purple;
        font-size: 24pt;
      }
      a {
        color: blue;
        font-size: 120%;
      }
    </style>
  </head>
  <body>
    <h2>Font-size property</h2>
    <span>This text is written with 2vh font-size.</span>
    <p>This paragraph is written with 1em font-size.</p>
    <div class="length">Example with 30px font-size length </div>
    <h3>Example with 3ex font-size length.</h3>
    <h1>We set the font size 24pt  for this heading.</h1>
    <a href="https://www.w3docs.com/">This hyperlink is written with 100% font-size.</a>
  </body>
</html>

Try it Yourself »

Example of the font-size property with the absolute-size values:

<!DOCTYPE html>
<html>
  <head>
    <title>Title of the document</title>
    <style>
      .font-xxsmall {
        color: grey;
        font-size: xx-small;
      }
      .font-xsmall {
        color: grey;
        font-size: x-small;
      }
      .font-small {
        color: grey;
        font-size: small;
      }
      .fontSize-medium {
        color: grey;
        font-size: medium;
      }
      .font-large {
        color: grey;
        font-size: large;
      }
      .font-xlarge {
        color: grey;
        font-size: x-large;
      }
      .font-xxlarge {
        color: grey;
        font-size: xx-large;
      }
    </style>
  </head>
  <body>
    <h1>Font-size property</h1>
    <div class="font-xxsmall">Example with font-size xx-small property</div>
    <div class="font-xsmall">Example with font-size x-small property</div>
    <div class="font-small">Example with font-size small property</div>
    <div class="font-medium">Example with font-size medium property</div>
    <div class="font-large">Example with font-size large property</div>
    <div class="font-xlarge">Example with font-size x-large property</div>
    <div class="font-xxlarge">Example with font-size xx-large property</div>
  </body>
</html>

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Example of the font-size property with "smaller" and "larger" values:

<!DOCTYPE html>
<html>
  <head>
    <title>Title of the document</title>
    <style>
      .smaller {
        color: red;
        font-size: smaller;
      }
      .larger {
        color: red;
        font-size: larger;
      }
    </style>
  </head>
  <body>
    <h1>font-size property</h1>
    <div class="smaller">Example with font-size smaller property</div>
    <div class="larger">Example with font-size larger property</div>
  </body>
</html>

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Values

Value	Description	Play it
medium	Sets the font-size to medium. This is the default value of this property.	Play it »
xx-small	Sets the font-size to xx-small.	Play it »
x-small	Sets the font-size to x-small.	Play it »
small	Sets the font-size to small.	Play it »
large	Sets the font-size to large.	Play it »
x-large	Sets the font-size to x-large.	Play it »
xx-large	Sets the font-size to xx-large.	Play it »
smaller	Smallers the font-size.	Play it »
larger	Largers the font-size.	Play it »
length	Specifies the font-size by px, em etc.	Play it »
%	Sets the font-size to a percent of the parent element's font size.	Play it »
initial	Makes the property use its default value.	Play it »
inherit	Inherits the property from its parents element.