About this calculator
Enter a value and the root font size, usually 16 px.
How to use it
- Choose the direction.
- Enter the value.
- Enter the root font size.
The formula
rem = px ÷ root font size; px = rem × root font size
- root font size
- the html element’s font size, 16 px by default
Worked example
24 px at a 16 px root
- 24 ÷ 16 = 1.5rem.
What the result means
Using rem for text and spacing helps accessibility.
Assumptions
- Root size in pixels.
Limitations
- em units depend on the parent element instead.
Frequently asked questions
How many px is 1 rem?
16 px by default.
What is 14 px in rem?
0.875rem at a 16 px root.
rem or em?
rem is relative to the root; em to the parent.
Last reviewed on 3 October 2026. Found a mistake? Tell us.