Converter
Convert CSS values across absolute and relative units with the same context your layout actually uses: root font size, parent font size, and viewport dimensions.
Best use case
This works best when you need more than simple px-to-rem math and want one place to compare type, spacing, and viewport-based values under real layout settings.
Common values
Start from a typical typography or spacing value if you want a faster sanity check first.
Value to convert
Better CSS unit tools let you choose the source unit first instead of assuming every conversion begins from pixels.
Used for rem calculations.
Used for em and % values.
Used for vw conversion.
Used for vh conversion.
Source
16px
Pixel baseline
16px
Context summary
rem uses 16px, em and % use 16px, and viewport units use 1440×900.
Conversion results
Review every output together so you can compare spacing, typography, and viewport sizing without re-entering the value.
Pixels
Absolute web unit
16px
Root EM
Based on html font size
1rem
Parent EM
Based on parent font size
1em
Percentage
Relative to parent size
100%
Viewport width
Based on screen width
1.1111vw
Viewport height
Based on screen height
1.7778vh
Points
Useful for print handoff
12pt
How to Use This CSS Unit Converter
Start from the unit you already have, set the layout context around it, then compare the full conversion table before you copy the exact value you want to ship.
Enter the value and source unit
Start from the unit you already have, whether that is px from a mockup, rem from a design system, or viewport units from a responsive layout.
Set the layout context
Adjust the root size, parent size, and viewport dimensions so the relative conversions reflect the way your real interface behaves.
Review all output units together
Compare px, rem, em, percent, vw, vh, and pt side by side to see how one value translates across typography, spacing, and responsive layout work.
Copy the exact unit you need
Take the converted value directly into your CSS, token file, design handoff notes, or debugging workflow.
When This Tool Is Most Useful
It helps most when you are translating mockup values into maintainable CSS or trying to understand how a spacing or typography choice changes under different responsive contexts.
Typography conversion
Translate body text, labels, and heading sizes between px, rem, and em when you are moving from mockups into scalable CSS.
Spacing and layout systems
Compare padding, margins, and gaps across absolute and relative units so your spacing system scales more predictably.
Responsive viewport checks
See how fixed values translate into vw or vh when you are building fluid sections, hero layouts, or viewport-based patterns.
Print and handoff conversions
Use points when you need a quick bridge between web values and print-adjacent or documentation-oriented output.
FAQs
Why include both rem and em?+
rem depends on the root font size, while em depends on the parent element. Seeing both together helps when you work inside component systems and global typography scales.Why ask for viewport width and height?+
vw and vh are not fixed multipliers, so the converter needs viewport dimensions to give useful real values.What is this most useful for?+
It is useful for typography scaling, spacing systems, responsive layout debugging, and converting design values into more maintainable CSS units.Why include percentage output as well?+
Percentage values are still common in layout work, and showing them with em and rem makes relative sizing decisions easier to compare.