Rem vs Px: What’s the Difference for Your Website?

Pixels and rem are commonly used terms in web development, and understanding them is key to building high-quality websites. In this article, we’ll explain what they are and why it’s important to grasp the difference between the two.

Pixel: Definition

Pixels are a widely used unit of measurement in web development, as they allow you to define an element’s size on a screen with absolute precision. For this reason, pixels are a popular choice for developers seeking full control over element sizing on their website.

Using Pixels

When you use pixels to define element sizes on your website, you can be certain the element will have exactly the same size across all screens. However, this can also cause issues if you want your website to be responsive and display correctly on screens of different sizes. Pixels are fixed and do not automatically adapt to varying screen dimensions.

Advantages of Pixels:

- Absolute precision in element sizing

- Full control over element dimensions

Despite these advantages, pixels can create problems if you want your website to display properly on screens of different sizes. It’s therefore important to weigh the pros and cons before deciding to use pixels for your website’s design.

The problem goes beyond responsive design, and it has a normative counterpart. Success criterion 1.4.4 “Resize Text” in the WCAG, at level AA, requires text to be enlargeable up to 200% without loss of content or functionality. A size in pixels ignores the font-size preference a user has set in their browser: someone with low vision who set their browser to 24px will still read 14px text on your site. That is the use case that settles the debate, far more than adapting to screen sizes.

Rem: Definition

Rem is a relative unit of measurement based on the font size of the root element, the html tag, to define an element's size. That is what sets it apart from em, which refers to the font size inherited from the parent element: a common confusion, and a consequential one. Rem units are thus more flexible than pixels and automatically adapt to different screen sizes.

This is where the real argument sits, and it goes beyond responsive layout. The root element's default value is 16 pixels in browsers, but user preferences can change it. Someone with low vision who raises their browser's default font size will see a rem-based site adapt, while a px-based site stays frozen. This is not a comfort detail: WCAG success criterion 1.4.4 "Resize Text", at level AA, requires that text can be resized up to 200% without loss of content or functionality. Using px for typography is the simplest way to fail it. Sources: MDN documentation on CSS length units and W3C WCAG 1.4.4.

Using Rem

When you use rem to define element sizes on your website, you can be sure the element will have a consistent size across all screens. This means your website can display correctly on screens of varying sizes, which is crucial for user experience.

One point of arithmetic avoids the most common mistake: rem always refers to the root element’s font size, unlike em, which refers to the parent element’s and therefore compounds at every level of nesting. MDN’s font-size documentation details that difference and explicitly advises against setting the root size in percentages or pixels if you want to respect the user’s setting. In practice: leave the root element at its default value, express text sizes in rem, and keep pixels for elements that genuinely must stay fixed, such as a one-pixel border.

Advantages of Rem:

- Flexibility to adapt to different screen sizes

- Ensures an optimal user experience across all screen types

Using rem units gives you better control over how your website displays across different screen sizes, which is crucial for responsive design and an optimal user experience. However, it’s worth noting that rem can be more challenging for beginner developers, as they require an understanding of the root element’s font size and how it affects element sizing on the web.

Rem or pixel?

Pixels and rem are two different units of measurement used to define the size of elements on a website. Pixels provide absolute precision for element sizing but can cause issues if you want your site to display correctly across different screen sizes. Rem, on the other hand, are more flexible and automatically adapt to various screen sizes, ensuring an optimal user experience.

It’s important to understand the advantages and drawbacks of each unit to determine what’s best for your specific website. If you need total control over the size of precise elements, pixels may be the right choice. But if you want your site to display correctly across different screen sizes, rem should be preferred.

CSS clamp() and fluid typography in 2026

Beyond the rem/px choice, CSS clamp() introduces a third approach: fluid values. The clamp(min, preferred, max) syntax defines a size that adapts to the screen width without media queries.

Practical example: font-size: clamp(1rem, 2.5vw, 1.5rem) sets a font size of 16px on mobile, which scales proportionally up to 24px on desktop. No need to write two separate media queries for text sizing.

Container queries (CSS @container) go further: they allow you to adapt a component’s style based on its parent container’s size, not the viewport. On Webflow, native CSS variables (since 2024) let you centralize these values and modify them in one place.

How many rem is 1 pixel?

In reality, the answer depends on the browser and the root element’s font size defined on a website. By default, the root element’s font size is set to 16 pixels, meaning an element defined as 1 rem will be 16 pixels. However, the root element’s font size can be set to a different value, which will affect how many rem 1 pixel equals.

Example of rem to pixel conversion

For example, if the root element's font size is set to 10 pixels, an element defined as 1 rem will be 10 pixels. If it is set to 20 pixels, that same element will be 20 pixels. Nesting depth makes no difference: unlike em, the value does not compound from one parent to the next.

In other words, the number of rem that make up 1 pixel depends on the font size of the root element, set by the site or by the browser. There’s no standard answer, as it depends on how the site or browser is configured.

On Webflow, the tool handles the conversion itself!

When developing your site on Webflow, you can directly convert pixels to rem. To do this, simply add "/16" after the pixel value in the designer where you usually input pixels, and it will convert to rem. Alternatively, you can download an extension like Finsweet to convert the entire page automatically.

With Scroll agency, opt for a 100% responsive website

At Scroll, we are Webflow experts and that’s why we’ve built the Webflow agency to support you in creating your website. Our solutions are bespoke and 100% responsive to adapt to all devices. No need to worry about pixel-to-rem conversion, our experts handle everything for you. If you have a new website or redesign project, feel free to contact us!