REM versus EM
Use REM for spacing or typography that should follow the document root consistently. Use EM when a component should scale from its own inherited font size, and remember that nested EM calculations can compound.
Developer tool
PX to REM & EM Converter
Convert pixel values to rem or em instantly. Set your base font size and copy clean CSS-ready values.
Convert CSS units against an explicit base
REM values use the root font size, while EM values are relative to the relevant element context. The calculator makes the arithmetic immediate, but the correct base still depends on the CSS where the result will be used.
Batch replacement
The batch field helps translate several pixel values using one base. Review media queries, borders and values that intentionally remain in px rather than replacing every number without context.
Result
1.5rem
24px = 1.5rem
Popular values for 16px base
4px = 0.25rem
8px = 0.5rem
12px = 0.75rem
14px = 0.875rem
16px = 1rem
18px = 1.125rem
20px = 1.25rem
24px = 1.5rem
32px = 2rem
40px = 2.5rem
48px = 3rem
64px = 4rem
Batch converter
Convert px values in CSS to rem
Frequently Asked Questions
What does the base font size control?
It is the divisor for PX-to-REM or PX-to-EM calculations. A 16 px value equals 1 rem when the root base is 16 px.
Are REM and EM always interchangeable?
No. REM refers to the root font size, while EM depends on the current element context and can compound through nesting.
Should every pixel value be converted?
No. Borders, raster alignment and fixed technical constraints may intentionally stay in pixels. Convert only values that should scale with typography.
Does the tool modify my CSS file?
No. It calculates and formats values for copying; it does not upload, parse or overwrite a stylesheet.