25 rem to px = 400px
25 rem equals 400 pixels at the default root font size of 16px. Adjust the root size below to recalculate.
What’s 25rem used for?
25rem (400px at default root) sits at the layout-token scale rather than spacing — used for component widths like card max-widths, modal dialogs, or sidebar fixed widths. At 16px root it equals 400px, a common 'narrow column' width for prose readability or focused dialog content.
How it works
To convert 25rem to pixels, multiply by the root font size: 25 × 16 = 400. The rem unit is relative to the root element’s font size, which browsers default to 16px.
25rem at different root sizes
If you’ve overridden the html root font size, the pixel equivalent of 25rem shifts. Here’s 25rem at common root sizes.
| Root size | 25rem in px |
|---|---|
| 16px (default) | 400px |
| 12px | 300px |
| 14px | 350px |
| 18px | 450px |
| 20px | 500px |
| 24px | 600px |
25rem in CSS
Use 25rem as a content max-width — 400px at the default root.
.prose {
max-width: 25rem; /* 400px at 16px root */
margin-inline: auto;
}FAQ
Is 25rem the same as 400px?
Yes, at the browser default root font size of 16px. If the root has been changed (some sites use html { font-size: 62.5% } or similar), the conversion changes — see the table above for 25rem at other root sizes.
Why use 25rem instead of 400px?
Because 25rem scales with the user’s browser font-size preference, and 400px does not. If a user enlarges their default font size for accessibility, anything sized in rem scales proportionately — including this value. Use rem for type and type-adjacent properties; reach for px only when the value must stay fixed regardless of user settings.