What Are the Bootstrap 4 Text Font Sizes and How Do You Change Them?

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Bootstrap’s font sizes are calculated off of the body font size by using rem values. If you change the body font size all styles will be increased/decreased automatically. Rem stands for “root em” because it calculates the size based on the size of the root of the document or body tag.

So Bootstrap’s global default font-size is 16px.

1rem = 16px

Default styles applied to the body of the document

BodyStyles
bodyfont-size: 16px;

line-height: 1.5;

font-family: “Helvetica Neue”, Helvetica, Arial, sans-serif;

Bootstrap 4 Text Sizes

Tag / ClassFont Size
p1rem / 16px
h12.5rem / 40px
h1 small80% / 32px
h22rem / 32px
h2 small80% / 25.6px
h31.75rem / 28px
h3 small80% / 22.4px
h41.5rem / 24px
h4 small80% / 24px
h51.25rem / 20px
h5 small80% / 16px
h61rem / 16px
h6 small80% / 12.8px
.display-16rem / 90px
.display-25.5rem / 82.5px
.display-34.5rem / 67.5px
.display-43.5rem / 52.5px

How to Increase the Default Bootstrap Font Size

The default font-size for Bootstrap is 1rem. This converted to the pixel equivalent is dependent on the default font-size of the browser. The majority of browsers today use 16px, but this can vary for older browsers.

To change the default font size, add this CSS rule to your theme stylesheet after the Bootstrap stylesheet.

How to Change the Bootstrap Font Family for All Headlines

Add a google font stylesheet below the Bootstrap CSS stylesheet.

<link href="https://fonts.googleapis.com/css?family=Oswald" rel=“stylesheet”>

Add this to your theme stylesheet to override Bootstrap’s default values.

How to make Bootstrap 4 Font Sizes Responsive

In Bootstrap version 4.3 they introduced responsive font sizes. This featured is turned off by default but can be enabled when you compile your own version of the Sass source files. You can learn more about this feature in the GitHub repo documentation.

Summary

So as you can see, changing the document font size and font family is pretty easy because Bootstrap uses rems for typography font sizes. If you change the default body font size of 16px all headings and paragraphs will adjust off of that size. If you need more variation, you will need to write new CSS classes to specify new rem values to override what Bootstrap is using. A good way to do this is to look at the typography styles and write your overrides in a separate document.

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Written by: Jacob Lett
Category: Common Questions
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