CSS Unit Converter - PX to REM, EM, Percent Online

📐 Base Font Size: px This is typically set on the html or body element. Default browser value is 16px.

🔄 Enter a value in any field to convert

Pixels

Absolute unit, fixed size

Root EM

rem

Relative to root font size

Relative to parent font size

Percent

Relative to parent element

Points

1pt = 1/72 inch (print)

Viewport Width

1vw = 1% viewport width

📊 Quick Reference (Base: 16px)

Pixels	REM	EM	Points

📖 Understanding CSS Units

Absolute Units

Pixels (px): The most common unit. 1px is typically 1/96th of an inch on screens. Pixels don't scale with user preferences, which can be an accessibility concern.

Points (pt): Traditionally used in print (1pt = 1/72 inch). Not recommended for screen design.

Relative Units

REM: Relative to the root element's font size (usually 16px). Best for consistent, scalable designs. If a user changes their browser font size, rem-based layouts will scale accordingly.

EM: Relative to the parent element's font size. Can compound (nested elements multiply), which can lead to unexpected sizes.

Percent (%): Relative to the parent element. Commonly used for widths and responsive layouts.

VW/VH: Relative to viewport dimensions. 1vw = 1% of viewport width. Great for full-screen sections and responsive typography.

💡 Pro Tip: Use rem for font sizes and spacing to ensure accessibility. Users who increase their browser's default font size will have a properly scaled experience.

🎯 Best Practices

Typography: Use rem for font-size, ensuring scalability
Spacing: Use rem or em for padding and margins
Layouts: Use %, vw, or flexbox/grid for responsive widths
Borders: px is acceptable for thin borders (1-2px)
Media queries: Use em for breakpoints (they scale with zoom)

❓ Frequently Asked Questions

rem is always relative to the root (html) element's font size. em is relative to the parent element's font size, which can compound. For example, if you have nested elements each set to 1.5em, the inner text will be 1.5 × 1.5 = 2.25 times the base size.

16px is the default font size in most browsers. When users don't customize their browser settings, 1rem = 16px. This is why it's the standard base for calculations.

For accessibility and responsive design, prefer rem for font sizes and spacing. Use px only for elements that should stay fixed regardless of user preferences, like thin borders or box shadows.