Why Use REM instead of Pixels?
In modern web development, accessibility and responsive design are critical. Hardcoding sizes using Pixels (`px`) forces text and layout elements to remain a fixed size, regardless of what the user might prefer.
Using **REM (Root EM)** solves this. REM units are relative to the root `` font size. By default, most browsers set the root font size to `16px`. Therefore, `1rem` equals `16px`. If a visually impaired user increases their browser's default font size to `24px`, all elements styled with REMs will naturally scale up to accommodate them, whereas pixel-based layouts will stay stubbornly small.
The Difference Between REM and EM
While both REM and EM are relative units, they behave differently:
- REM (Root EM): Always relative to the root element (`html`). It is consistent and predictable across the entire document.
- EM: Relative to the font size of the parent element. This can lead to the "compounding problem." If you have nested `
`s all set to `1.2em`, the text will get exponentially larger the deeper it is nested. EM is best used for sizing components like padding or margins relative to their own text size, not for global layouts.
Common Pixel to REM Conversions
Assuming the standard base size of `16px`, here are common conversions used in UI design:
| Pixels (px) |
REM |
| 12px |
0.75rem |
| 16px (Base) |
1rem |
| 24px |
1.5rem |
| 32px |
2rem |