Pixel to REM Converter

Convert between pixels and rem units instantly. Adjust your base font size, view a full conversion table, and generate responsive typography scales for your CSS projects.

How to Convert Pixels to REM

Converting pixels to rem is a fundamental skill for modern web development. The formula is straightforward: take your pixel value and divide it by the root font size. With the browser default of 16px, converting 24px to rem gives you 24 / 16 = 1.5rem. This converter handles the math automatically, including non-standard base font sizes.

REM stands for "root em" and is one of the most important CSS units for building responsive, accessible websites. Unlike pixels, which are absolute and fixed, rem units scale relative to the root element's font-size property. This means your entire layout can adapt when users change their browser font settings or when you adjust the base size for different breakpoints.

PX, REM, EM, and More

CSS provides several unit types for defining sizes, spacing, and typography. Each has specific use cases and behavior that affects how your designs render across devices and user configurations.

Pixels (px)

Pixels are the most intuitive unit because they map directly to screen pixels (with some nuance for high-DPI displays). A value of 16px always renders at the same size regardless of context. While simple to use, pixels do not scale with user preferences, which can cause accessibility issues. Users who increase their browser's default font size will not see pixel-defined text grow larger.

REM (Root EM)

REM units are relative to the html element's font-size. If the root font-size is 16px (the browser default), then 1rem = 16px, 2rem = 32px, and 0.5rem = 8px. The key advantage of rem is consistency: no matter how deeply nested an element is, 1rem always equals the same value. This makes rem ideal for typography, spacing, and layout dimensions.

EM

EM units are relative to the font-size of the parent element. This creates a compounding effect: if a parent has font-size: 1.2em and a child also has font-size: 1.2em, the child renders at 1.44x the base size. While useful for component-level scaling, this compounding can be confusing. Many developers prefer rem for predictability.

Percentage (%)

Percentage values are relative to the parent element's corresponding property. For font-size, 100% equals the parent's font-size. For width, 100% equals the parent's width. Percentages are essential for fluid layouts and are commonly combined with rem for comprehensive responsive design.

Viewport Units (vw, vh)

Viewport width (vw) and viewport height (vh) units represent 1% of the viewport dimension. So 50vw is half the viewport width. These units are powerful for full-screen layouts and fluid typography, but should be used carefully as they do not respect user font-size preferences. A common pattern is using clamp() with vw units and rem min/max values for fluid type that still respects accessibility.

Why Use REM Over Pixels?

There are several compelling reasons to adopt rem as your primary CSS unit:

• Accessibility: rem respects user browser font-size settings. Users with visual impairments often increase their default font size, and rem-based layouts honor that choice.
• Scalability: changing the root font-size in a media query scales your entire layout proportionally, making responsive design much simpler.
• Maintainability: using a consistent unit system makes it easier to reason about spacing and sizing relationships across your codebase.
• Design tokens: rem values map naturally to design token systems. A spacing scale of 0.25rem, 0.5rem, 1rem, 1.5rem, 2rem creates predictable, harmonious layouts.

The 62.5% Trick

Some developers set html { font-size: 62.5%; } which makes 1rem equal to 10px (62.5% of the 16px default). This simplifies mental math: 1.6rem = 16px, 2.4rem = 24px, and so on. While convenient, this approach requires you to explicitly set the body font-size back to 1.6rem so paragraph text remains readable. Our converter supports any base font size, so you can use this trick or any custom value.

Responsive Typography Scales

A typography scale is a set of harmonious font sizes based on a mathematical ratio. Common ratios include the Major Third (1.250), Perfect Fourth (1.333), and the Golden Ratio (1.618). Starting from a base size (usually 16px or 1rem), each step in the scale multiplies by the ratio. For example, with a Major Third scale, the sizes would progress: 16px, 20px, 25px, 31.25px, and so on.

Using the scale generator above, you can create a complete set of CSS custom properties for your project. Apply these as variables throughout your stylesheet to maintain typographic consistency. Adjust the ratio and base size to match your design requirements.

Tips for Using REM in Your Projects

• Set your base font-size on the html element, not the body. This ensures rem calculations are consistent.
• Use rem for font-size, margins, padding, and max-width. Reserve px for borders, shadows, and tiny details where scaling is not desired.
• Combine rem with CSS clamp() for fluid typography: font-size: clamp(1rem, 2.5vw, 2rem) creates text that scales smoothly between breakpoints.
• Define spacing scales using CSS custom properties with rem values. This creates a single source of truth for your spacing system.
• Test your layouts by changing the browser's default font size. If your design breaks, you likely have some pixel-based values that should be rem instead.
• When converting an existing pixel-based design to rem, use a converter tool like this one to batch-convert your values and update your stylesheets systematically.

Common Pixel to REM Conversions

Here are the most frequently used conversions with a 16px base. These cover the majority of font-size, spacing, and dimension values you will encounter in web development:

• 8px = 0.5rem (small spacing, icon padding)
• 12px = 0.75rem (caption text, small labels)
• 14px = 0.875rem (secondary text, form labels)
• 16px = 1rem (body text, base size)
• 18px = 1.125rem (large body text)
• 20px = 1.25rem (h4 heading)
• 24px = 1.5rem (h3 heading, card padding)
• 32px = 2rem (h2 heading)
• 48px = 3rem (h1 heading)
• 64px = 4rem (hero heading)

Using REM with CSS Media Queries

One advanced technique is adjusting the root font-size at different breakpoints. For example:

Set html font-size to 14px on mobile (under 768px), 16px on tablet (768px to 1024px), and 18px on desktop (above 1024px). Since all your rem-based sizes reference the root, the entire layout scales proportionally at each breakpoint. This approach reduces the number of individual property overrides you need in your responsive CSS.

Community Questions

• How to convert pixels to rem in CSS? 15 answers · tagged: css, px, rem
• Why use rem instead of px for font sizes? 12 answers · tagged: css, rem, responsive
• What is the default root font size for rem? 9 answers · tagged: css, rem, typography

Frequently Asked Questions