Which CSS Unit is Best for Margins and Padding in WordPress Plugins?

When you’re building a WordPress plugin and styling your elements, you’ll often use CSS unit to add space around things — like margins and padding. But choosing the right unit can be confusing. Should you use px, em, or rem?

Let’s explain it simply.

Use rem for Most Spacing

The best CSS unit for margins and padding is rem. It stands for “root em”, and it’s based on the root font size of the browser. Most browsers have a default font size of 16px, so 1rem usually equals 16px.

Example:

padding: 1rem; /* = 16px */
margin-bottom: 2rem; /* = 32px */

Using rem helps make your plugin design more flexible and accessible. If a user increases their browser font size for easier reading, the spacing will scale too — keeping your layout clean on all devices.

When to Use px

px stands for pixels, which are fixed CSS units. It gives you exact control over spacing, but it doesn’t scale with screen size or user settings.

Use px for:

• Borders (like 1px solid #ccc)
• Box shadows
• Icon sizes or pixel-perfect UI tweaks

Tip: Avoid Mixing Too Many Units

For a clean, responsive design:

• Use rem for spacing (padding, margin)
• Use rem for font size
• Use px for small details (borders, shadows)
• Use unitless or em for line height

Conclusion:
If you want your plugin to be responsive, accessible, and look good on all screen sizes, make rem your default for spacing. It’s simple, scalable, and future-proof.