TYPE & SPACING STUDIO

PX to REM Workbench

Convert pixels to rem with a custom root font size, inspect the formula and copy CSS. Test accessible typography and spacing without uploading design data.

Choose root size → Enter pixels → Copy CSS

FOR REPEATED BATCH WORK

CSS Sizing Batch Kit

Turn a CSV of pixel measurements into reusable CSS custom properties.

Planned price: $3 one-time. Checkout is not available yet. The browser tool above is free.

See what is included in the $3 kit

Python 3.10+ command-line tool, standalone browser converter, sample token CSV, README and internal-use license. Names are checked; outputs round to six decimal places.

No subscription, custom service or future updates are promised.

Download Sample token CSV free

How to read your result

REM values are relative to the computed font size of the root html element. At a 16px root, 24px is 1.5rem; at 20px it is 1.2rem. Relative units alone do not guarantee accessibility: test browser zoom and real content. Negative values suit margins, not font sizes.

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Reproduce a known result

1.2 rem. The CSS file assumes the page already has a computed 20px root; it does not override browser preferences.

Load 24px at a 20px root · Download synthetic example

Examples and troubleshooting

REM conversion is division: rem = pixels ÷ root font size in pixels. The important input is the computed font size of the root html element. A convenient 16px assumption is not a measurement of every page.

PX to REM conversion with 16px and 20px root sizes

Common questions

Is 16px always the root font size?

No. Read the computed html font size for the page you are changing. The converter lets you set that value explicitly.

What is the difference between rem and em?

REM uses the root font size. EM depends on the relevant element's font size and the property being evaluated; nested rules can behave differently.

Can I convert a negative value?

Yes, when the destination CSS property allows it, such as certain margins. The root size must remain positive.

Privacy and anonymous measurement

Your tool inputs stay in the isolated browser workspace. We count page views and action names, anonymous browser IDs, referring domain, campaign channel and device class. We do not collect your JSON, email text, playlists or complete referring URLs. Country is unknown unless supplied by a trusted server configuration. Browser storage may be unavailable; in that case unique-user counts are limited to this visit.