CSS Unit Converter
Convert common CSS units using your base font size, parent size, and viewport dimensions.
Translate CSS units with context
CSS length units only look simple until you try to convert them, because most are relative to something.
rem depends on the root font size, em on the parent, vw and vh
on the viewport dimensions, and % on a containing size. Convert without pinning those down and you get
numbers that are subtly wrong. This tool puts every assumption in one place — base font size and viewport width and
height — and converts your value into all six units at once.
That makes it genuinely useful for building responsive type scales, translating a pixel spec into
viewport-relative units for fluid layouts, or double-checking why an em value is compounding
unexpectedly. Change any assumption and every result recalculates instantly.
Private and instant
All math runs locally in your browser — nothing is uploaded, and the full set of conversions updates as you type.
Frequently Asked Questions
Which units are supported?
px, rem, em, vw, vh, and percent are included.
Why do I need viewport settings?
vw and vh depend on viewport width and height, so the converter needs those values.
Why do percent values need a parent size?
Percent lengths are relative to a parent or context size, not an absolute global value.
Need a polished interface, not just generated CSS snippets? Let us build it.