CSS Unit Converter
Convert between PX, REM, EM, and % CSS units instantly.
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Buy me a coffeeWhat is CSS Unit Converter?
CSS units determine the size of elements on web pages. Different units serve different purposes: PX (pixels) are fixed units, REM units scale relative to the root font size (usually 16px), EM units scale relative to the parent element's font size, and percentages are relative to the parent element. Our converter helps you quickly translate between these units for responsive design and accessibility compliance.
How to Use CSS Unit Converter
Common Use Cases
- Converting fixed pixel designs to responsive REM units
- Calculating accessible font sizes for WCAG compliance
- Converting designer specs (PX) to fluid layouts
- Understanding relative unit relationships
- Building scalable component systems
Frequently Asked Questions
What is the difference between REM and EM?
REM units are relative to the root element's font size (usually 16px), making them consistent throughout the page. EM units are relative to the parent element's font size, which can compound and make calculations complex.
Why use REM instead of PX?
REM units respect user font size preferences in browsers, improving accessibility. They also make responsive design easier since changing the root font size scales the entire layout proportionally.
What base font size should I use?
The browser default is 16px, which is the standard. However, some designers use 10px for easier mental math (1rem = 10px). Always test with different user font size settings.