What is the standard base font size for REM calculation?

The standard browser default root font size is 16px (1rem = 16px). You can customize this base in the tool if your CSS sets html { font-size: 62.5%; } (10px base) or other scales.

What is the difference between REM and EM?

REM (Root EM) is relative to the root element font-size, whereas EM is relative to the font-size of its immediate parent container.

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Converters

PX to REM & EM Converter

Convert pixels to REM, EM, VW, VH, and CSS units

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Aspect Ratio Calculator

Calculate 16:9, 4:3, 21:9 image and video aspect ratios with proportional resizing

CSS Grid Layout Generator

Create custom CSS Grid layouts with column/row spans, gaps, and interactive preview

CSS clamp() Fluid Calculator

Calculate fluid responsive typography and spacing CSS clamp() values

How to Use PX to REM & EM Converter

Set your project root font size (default is 16px).
Type a pixel value (PX) or REM value into either box for instant bi-directional conversion.
Review the calculated EM, %, PT, VW, and VH values.
Click the Copy button next to any unit value to paste it into your CSS.

Frequently Asked Questions

What is the standard base font size for REM calculation?: The standard browser default root font size is 16px (1rem = 16px). You can customize this base in the tool if your CSS sets html { font-size: 62.5%; } (10px base) or other scales.
What is the difference between REM and EM?: REM (Root EM) is relative to the root <html> element font-size, whereas EM is relative to the font-size of its immediate parent container.

Sources & References

Primary references: MDN: clamp() CSS function; WHATWG HTML Living Standard.

Review policy: references and behavior notes are checked whenever the tool implementation changes.