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px to rem
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px to em
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px to pt
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px to vw vh
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rem to px
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em to px
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pixel density
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About CSS Tools
CSS unit converters are essential for web developers and designers building responsive, accessible layouts. Choosing the right unit—pixels, rem, em, or viewport units—has a direct impact on how your design scales across devices and user accessibility settings.
Why CSS Units Matter for Accessibility
Fixed pixel values do not respond to a user's browser font size preferences. Users who need larger text—often older users or those with visual impairments—set their default browser font size higher than 16px. If your layout uses px for typography and spacing, it will override these settings. REM and EM units scale correctly, making your design WCAG 2.1 compliant.
PX vs REM vs EM: A Practical Guide
Pixels (px) are absolute units—ideal for border widths and thin lines that should not scale. REM (Root EM) is relative to the root HTML font size (default 16px) and scales globally. EM is relative to the current element's font size, useful for component-level spacing. Viewport units (vw, vh) are relative to the browser window—ideal for hero sections and full-screen layouts.
How to Convert PX to REM
The formula is simple: REM = PX ÷ Root Font Size. At the browser default of 16px, 24px becomes 1.5rem. If a user has set their browser to 20px, your 1.5rem element automatically becomes 30px—respecting their preference. Use our PX to REM converter to translate all your fixed pixel values instantly.
Frequently Asked Questions
What is the default root font size in CSS?
The default root font size in all major browsers is 16px unless overridden by the user or by CSS on the html element.
Should I use REM or EM for spacing?
Use REM for global spacing (padding, margin) to maintain consistency. Use EM for component-internal spacing so it scales proportionally with the component's own font size.
What is 1rem in pixels?
At the browser default of 16px, 1rem = 16px. If the user changes their browser font size to 18px, 1rem = 18px automatically.