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PX to EM/REM Converter - Online Responsive Unit Calculator

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PX to EM/REM Converter

Responsive CSS Unit Calculator — Convert pixels to relative units instantly

PX
PX
PX
EM
1.5
24px ÷ 16px = 1.5em
REM
1.5
24px ÷ 16px = 1.5rem
QUICK PX VALUES
PX
PX
24
1.5em × 16px = 24px
QUICK VALUES
Common PX to EM/REM Reference (based on current settings)
PX EM (base: 16px) REM (root: 16px)
Frequently Asked Questions
What is the difference between PX, EM, and REM?

PX (pixels) is an absolute unit — one pixel equals one dot on the screen. EM is relative to the font size of its parent element. REM (root EM) is relative to the root <html> element's font size, which defaults to 16px in most browsers. EM can cascade and compound in nested elements, while REM remains consistent throughout the document.

How do I convert PX to EM?

Divide the pixel value by the parent element's font size. Formula: EM = PX ÷ Parent Font Size (px). For example, if the parent font size is 16px and you want 24px, the result is 24 ÷ 16 = 1.5em. Use our converter above for instant calculations.

How do I convert PX to REM?

Divide the pixel value by the root font size (typically 16px). Formula: REM = PX ÷ Root Font Size (px). For example, 32px ÷ 16px = 2rem. If your project uses the 62.5% trick (html { font-size: 62.5%; }), the root size becomes 10px, so 32px ÷ 10px = 3.2rem.

What is the default browser font size?

All major browsers set the default root font size to 16px (equivalent to 100% or medium). This means 1rem = 16px unless you explicitly override it in your CSS. Users can change this in their browser settings for accessibility, which is why relative units like REM are recommended for responsive design.

Why should I use EM/REM instead of PX?

Relative units like EM and REM make your design responsive and accessible. When users change their browser's default font size, REM-based layouts scale proportionally. EM is useful for components that need to scale relative to their parent. PX values are fixed and don't respond to user preferences, potentially causing accessibility issues.

When should I use REM vs EM?

Use REM for global spacing, typography, and layout dimensions that should be consistent relative to the root. Use EM for component-level styling where elements should scale proportionally to their parent — like padding inside a button or margins within a card. For media queries, REM is preferred as it's consistent regardless of nesting.

What is the 62.5% font-size trick?

Setting html { font-size: 62.5%; } makes the root font size 10px (62.5% of 16px = 10px). This simplifies mental math: 1.4rem = 14px, 2.4rem = 24px, etc. However, some developers avoid this trick because it can interfere with user font-size preferences. Modern tools like this converter make it easy to calculate REM values with the default 16px base.

Does EM compound in nested elements?

Yes, EM values compound when nested. If a parent has font-size: 1.5em (24px at 16px base) and a child has font-size: 1.5em, the child's font size becomes 36px (24px × 1.5), not 24px. This cascading effect can make EM tricky in deeply nested structures. REM avoids this issue by always referencing the root element.

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