Font size refers to how large or small text appears on a website. It’s usually measured in pixels (px), ems (em), rems (rem), or percentages. Font size directly impacts readability, user experience, and how visitors engage with your content. Larger font sizes may be easier to read, but too large can overwhelm a layout, while too small can be tough to skim or understand.

Choosing the right font size is essential for balancing design aesthetics with accessibility. Good design ensures that headings, body text, and smaller details like captions have clear visual hierarchy. Whether you're creating a sleek landing page or a content-heavy blog, using consistent and scalable font sizing helps keep everything legible and well-structured.

Common units used to define font size

There are a few popular ways designers set font sizes, and each has its perks depending on the layout and responsiveness you want.

• Pixels (px) offer precision but aren’t as flexible for responsive design.
• Ems (em) are relative to the parent element’s font size, making them great for nested text elements.
• Rems (rem) are based on the root (html) element’s font size, offering more consistency across a site.
• Percentages (%) scale based on the default font size and are often used in combination with em or rem.

In modern web design, rem and em are preferred because they scale better across devices and improve accessibility. Understanding how these units work can save you time and frustration when tweaking your site’s design.

Why font size matters for UX and SEO

Font size isn’t just about looks—it’s tied directly to user experience and even SEO. Clear, readable text keeps people on your site longer and reduces bounce rates. If a visitor has to zoom in or squint to read, they’ll likely leave, and that sends poor signals to search engines.

Search engines also prioritize content that’s accessible and easy to engage with. Using proper font sizing across devices—especially mobile—ensures your message comes through clearly. This is especially important for blog posts, product descriptions, or service pages.

Best practices when setting font size

When designing your website, it’s helpful to start with a typographic scale. Set a base font size (often 16px) and scale headings up logically (like 1.25x or 1.5x). This keeps your layout clean and readable.

Here are a few other best practices:

• Use rem or em instead of px for better responsiveness.
• Make sure your body text is large enough to read comfortably on all screens.
• Maintain enough contrast between text and background.
• Test font sizes on mobile and desktop to ensure readability.

Tools like browser dev tools and accessibility checkers can help fine-tune your font sizing decisions.

How font size interacts with mobile responsiveness

Font size plays a big role in how your content looks on phones and tablets. Responsive design means text should automatically adjust depending on screen size. If you use rem or em units, it’s easier to scale fonts without needing custom styles for every device.

Most mobile-friendly website builders include default font settings that adapt across devices. But it’s always a good idea to preview your pages on different screens. For accessibility, WCAG recommends a minimum font size of 16px for body text.

Keeping your font sizes mobile-friendly ensures your content doesn’t just look good—it’s actually usable.

FAQs about font size

What is the best font size for a website?

There’s no one-size-fits-all answer, but a good starting point is 16px for body text. Headings should scale up from there to create hierarchy. Always test across devices and consider your target audience—older users may prefer slightly larger sizes.

Is px or rem better for font size in web design?

Rem is generally better for scalability and consistency, especially in responsive design. Px gives you more control, but doesn’t adapt as easily. Most modern web designers prefer rem because it allows for easier changes across your entire site.

Can font size affect SEO?

Yes, indirectly. If your text is too small or hard to read, users might bounce quickly, which hurts SEO. Good readability keeps people engaged and helps search engines understand that your content is valuable.

How do I change font size in my website builder?

Most website builders have built-in tools or theme settings that let you adjust font size for different elements like headers and body text. If you're using B12's AI website builder, it's as simple as a few clicks to adjust your text for readability and branding.

What font sizes should I use for mobile?

For mobile, body text should typically stay around 16px or scale appropriately if you’re using rem. Headings should remain bold and clear, but not take up too much screen space. Always test your layout on different devices to make sure it stays user-friendly.

Build better design foundations with B12

If you're working on a new site or redesigning one, getting your font sizes right from the start can make a huge difference. It’s a small design detail with a big impact on readability, conversions, and overall UX. Don’t leave your typography to chance—especially when tools like B12 make it easy to get it right.

Whether you’re launching a blog, portfolio, or full-service site, B12 helps you create a professional look without needing to code. Sign up to build your site with smart, accessible design baked in.