In web development, various units of measurement are used to define font sizes, margins, paddings, and other elements. The most common among them are px (pixels) and rem (relative units). Let's take a closer look at them.
PX (pixels)
px is an absolute unit of measurement that defines the size of an element in physical pixels on the screen. It does not depend on browser settings or font size.
Advantages:
- Predictability — the element will look the same on different devices (if the scale is not changed).
- Ease of use — there is no need to consider the nesting of elements.
Disadvantages:
- Does not account for user-defined scaling in the browser.
- Can be a problem for accessibility, as users may not be able to increase fonts through browser settings.
REM (relative units)
rem (root em) is a relative unit of measurement based on the font size of the root element (html).
How does rem work?
By default, browsers set the font size for html to 16px. Therefore:
-
1rem=16px(iffont-sizeforhtmlis not changed) -
2rem=32px -
0.5rem=8px
Advantages:
- Dynamic — by changing
font-sizeinhtml, all elements can be easily scaled. - Better accessibility support — users can change the font size through browser settings.
- Convenience in developing responsive designs.
Disadvantages:
- Requires understanding of the cascade of styles and document structure.
- Can complicate size calculations in complex layouts.
If you need precise positioning of elements, use px. If you want to make the design more responsive and accessible — rem will be the better choice.
On this page, you will find useful tools for quick conversions and more.
We also created an extension for the browser that will help you convert PX to REM and vice versa directly in the browser.