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Utilities

PX / REM Calculator Documentation

Use the free PX / REM Calculator →

Convert px to rem and rem to px with a configurable base font size, or switch to px to em for sizing relative to a parent font.

What does it do?

Convert px to rem and rem to px with a configurable base font size, or switch to px to em for sizing relative to a parent font.

How does it work?

SiteIndex divides or multiplies by the configured font size (16px by default). REM uses the root font size; EM uses the parent font size. PT converts at the CSS reference ratio of 96px per 72pt.

When to use it
  • Convert a design's pixel spacing into rem units for a CSS design system.
  • Check what a rem value equals in pixels at a custom base font size.
  • Build a quick reference table of common px-to-rem conversions.
Inputs and outputs
Input
Text, files, or values entered in the browser, depending on the tool.
Output
A result shown in the browser that can be reviewed or copied where supported.
Limitations
  • Results depend on the input, browser, network, and external service involved.
  • This tool is informational and does not replace specialist diagnostics.
Privacy and data handling

Inputs for this browser-side tool are processed locally and are not sent to SiteIndex. Normal page analytics may still be collected as described in the Privacy Policy. Read the Privacy Policy.

Results and sharing

Review the conversion and formula, copy the CSS-ready value, or select a reference size. Swap PX/REM to reverse. REM uses root font size; EM uses parent font size.

Use Share result to preview and copy a link. Anyone with the link can read the included details; nothing is saved on our server. Shared result links open read-only snapshots. Large results require a downloaded file instead.

How to use it

  1. Choose px to rem, rem to px, px to em, or pt to px.
  2. Enter the value and set the root or parent font size when applicable.
  3. Read the conversion and formula, or select a common reference value.
  4. Copy the CSS-ready result, or swap px and rem units to convert back.

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