Free PX to REM Converter — CSS Pixel to Root EM
November 3, 2026 · 3 min read · By the DollarWise team
How it works
Type a pixel or rem value, set your root font-size (16px by default), and this converter gives you the exact equivalent in the other unit — with the formula shown and a reference table of the most common CSS sizes, recalculated for whatever base you choose.
## How the math works
A rem ("root em") is equal to the font size of the root `` element. With the browser default of 16px, **1rem = 16px**, so:
**rem = px ÷ base font size** (and px = rem × base font size).
If you change the root font size — for example `html { font-size: 62.5% }` makes 1rem = 10px — every rem value scales automatically, which is why rems are preferred over pixels for accessible, responsive typography and spacing.
## Everyday uses
- **Design handoff:** convert a designer's pixel specs into rem values for your stylesheet.
- **Base-font changes:** switch a project to a 10px or 62.5% root and instantly recalculate every spacing token.
- **Accessibility audits:** verify that font sizes and spacing scale when a user overrides the default browser font size.
## Frequently asked questions
### Why use rem instead of px?
REM values scale with the user's chosen root font size, so text and spacing respect browser accessibility settings. Pixels are fixed and ignore user preferences. Most modern style guides recommend rem for typography and spacing.
### What if my project uses 62.5% root font size?
`html { font-size: 62.5% }` sets the root to 10px (62.5% of 16px), making 1rem = 10px so mental math is easy. Enter 10 as the base in this calculator to get correct conversions for that setup.
### What is the difference between rem and em?
`em` is relative to the current element's font size (so it compounds), while `rem` is always relative to the root `` element and never compounds. For consistent spacing and sizing across a layout, rem is usually the safer choice.