At the default root font size of 16px, 4px is exactly 0.25rem.
Calculation based on a root font-size of 16 pixels.
How to convert 4px to rem
To convert pixels to rem, divide the pixel value by the root font size: rem = px ÷ 16. For 4px that is 4 ÷ 16 = 0.25rem.
4px is a very small size, typically used for borders, hairlines, icon gaps and fine detail. It is often used for the smallest step of a 4px spacing grid.
4px at different root font sizes
| Root font size | Input | Result |
|---|---|---|
| 10px | 4px | 0.4rem |
| 12px | 4px | 0.3333rem |
| 14px | 4px | 0.2857rem |
| 15px | 4px | 0.2667rem |
| 16px | 4px | 0.25rem |
| 18px | 4px | 0.2222rem |
| 20px | 4px | 0.2rem |
| 22px | 4px | 0.1818rem |
| 24px | 4px | 0.1667rem |
CSS examples
font-size: 0.25rem; /* 4px */
padding: 0.25rem;
margin-bottom: 0.25rem;
width: 0.25rem;The same values in pixels, if you need a fixed size:
font-size: 4px;
padding: 4px;Tailwind CSS equivalent
The default spacing scale has a step for 0.25rem: use classes like p-1, m-1, gap-1, w-1 and h-1.
Nearby values
Frequently Asked Questions
4px equals 0.25rem when the root font size is the browser default of 16px. The calculation is 4 ÷ 16 = 0.25.
0.25rem equals 4px at a 16px root font size (0.25 × 16 = 4).
Yes. If the root font size is 18px, 4px equals 0.2222rem, and at 20px it equals 0.2rem. The pixel value itself never changes, only the rem equivalent. Use the base font size field above to try any value.
Prefer rem for font sizes, spacing and layout so they respect the user's browser font settings and scale for accessibility. Use px for details that should never scale, such as 1px borders or fixed icon sizes.