PX to REM
Convert individual values or CSS units with a custom root size.
Runs in your browser. Nothing is uploaded.
Why convert px to rem?
CSS pixels are useful when a value should describe a precise screen-sized detail, such as a border or a small icon adjustment. The rem unit is relative to the root element's font size. Spacing, type, and layout values expressed in rem can scale together when a user changes the browser's text size or when a design system changes its root scale.
A rem value is not automatically more accessible or more responsive. The right unit depends on the component, the browser behavior you want, and the rest of your CSS. Keep pixels when a fixed measurement is intentional, and use rem when a value should follow the root text scale. Check the result in the actual layout instead of converting every number mechanically.
The default base is 16px
This converter starts with a base font size of 16px because that is the common browser default for the root element. With that base, 16px becomes 1rem, 8px becomes 0.5rem, and 24px becomes 1.5rem. If your stylesheet changes html or uses a different root scale, enter that base before converting. The same base must be used when converting back from rem to px.
Results are rounded to four decimal places and trailing zeroes are removed. That keeps values such as 1rem readable while retaining enough precision for ordinary CSS spacing and typography. A rounded result is a practical representation, not a guarantee that a browser will render the same physical size on every display.
Convert values inside CSS
Paste a CSS snippet to convert every matching source unit in declarations. Comments and quoted strings are left alone, so a note such as /* 16px */ and generated content such as content: "16px" are not changed. Values without the selected source unit are preserved. You can copy the CSS output or download it as converted.css.
PX to REM is a unit converter, not a design-token system. It does not infer semantic names, group repeated values, choose a spacing scale, update variables, or check whether a converted value fits your component rules. Review custom properties, calculations, media queries, and browser fallbacks in the context of your project. For formatting and indentation, use the CSS Formatter.
Private local conversion
Numbers and CSS stay in your browser. Nothing is uploaded while you enter a base, paste a snippet, convert values, copy the result, or download a file. The tool does not fetch stylesheets or inspect your project, so it cannot know whether a declaration is overridden or whether a variable is defined elsewhere. Test the converted stylesheet in your normal build and browser checks.
FAQ
Can I convert a private CSS file without uploading it?
A dropped CSS file is read as text and converted in your browser. The stylesheet and numeric values are never uploaded, and TheDevTab never receives them.
What base font size does the converter use?
The default base is 16px, and the base must be a finite number greater than zero. Change it when the root element uses another font size and use the same base for the reverse conversion.
How is px converted to rem?
The converter divides the pixel value by the selected base font size. With a 16px base, 16px becomes 1rem and 8px becomes 0.5rem.
How is rem converted to px?
The converter multiplies the rem value by the selected base font size. With a 16px base, 1rem becomes 16px.
Which CSS values are changed in a stylesheet?
Only matching numeric values with the selected source unit are changed, and an identifier character immediately before the number prevents a match. Numbers inside block comments and quoted strings are copied unchanged.
Does this tool create design tokens?
No. It changes matching units only and does not infer semantic names, create variables, choose a spacing scale, or validate a stylesheet. The CSS structure and unrelated units are left as text.
How precise are the conversion results?
PX to REM results are rounded to four decimal places and trailing zeroes are removed. REM to PX uses the direct multiplication result without that rounding step, so review the displayed value when exact dimensions matter.