rem to px Calculator
Convert rem to px and back for CSS font sizes and spacing based on your root font size with this free web dev calculator in your browser.
Enter Values
Minimum 0
Minimum 0
Minimum 1
How to use this calculator
- Enter a value in rem or px.
- Set the root font size if it isn't 16 px.
How it works
px = rem × root font size; rem = px ÷ root font size.
Worked example
1.5 rem at 16 px root. = 24 px.
Common mistakes
- Forgetting the user's root size may differ from 16 px.
- Confusing rem (root-relative) with em (parent-relative).
Frequently asked questions
How do rem and px relate?
1 rem equals the root font size, 16px by default, so 1.5 rem is 24px. Change the base and the tool recalculates.
Should I use rem or px in CSS?
rem scales with the user's font settings, which helps accessibility, so it is preferred for type and spacing; px suits fixed details like borders.
Why use rem over px?
rem scales with the user's chosen base font size, which is better for accessibility.
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Cite this tool
Zerdly. (2026). rem to px Calculator. Retrieved from https://www.zerdly.com/tools/rem-to-px-calculator/
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.