PX to REM Calculator

A rem is a length unit equal to the root font-size of the page, which is set on the html element. If the root is 16px then 1rem is 16px and 1.5rem is 24px. Sizing in rem lets a whole layout scale from that single root value.

Divide the pixel value by the root font-size. At the common 16px root, 24px is 24 divided by 16, which gives 1.5rem. To go the other way, multiply the rem value by the root, so 1.5rem times 16 is 24px.

Every major browser applies 16px as the default font-size to the html element unless a stylesheet or the user overrides it. That makes 16px the standard baseline, which is why the root field starts there.

Yes. Set the root field to match your own CSS. Some teams set the root to 10px so 1rem equals 10px and conversions become tidy tenths, for example 32px becoming 3.2rem. The tool accepts any positive root value.

A rem is always relative to the root font-size, so it stays constant everywhere. An em is relative to the font-size of the current element, so it compounds when elements are nested. Rem avoids that surprise, which is why it is popular for global sizing.

Rem is preferred for type and spacing because it respects the user's chosen base font-size and scales the interface from one value, which helps accessibility. Px still suits fixed details like a one pixel border where scaling is unwanted.

Values are shown rounded to six decimal places with trailing zeros trimmed, so 24px at a 16px root reads as a clean 1.5rem. That precision is far finer than any pixel a browser will actually paint.

The root font-size must be a positive number, since dividing by zero has no meaning and a negative root is not valid CSS. If you enter one, the tool asks for a positive root instead of showing a result.

No. The conversion is plain arithmetic that runs entirely in your browser, so the values you type stay on your device and nothing is uploaded or logged.