CSS Unit Converter
Convert between px, rem, em, pt, and % using your base font size.
Every conversion runs locally in your browser. Nothing you enter here is sent to a server.
For informational and educational purposes only — not professional or technical advice, and not a substitute for consulting a qualified professional about your specific situation. TrueMeasureKit is not liable for decisions made based on these results. See our Terms of Service.
px vs. rem vs. em — when to use each
px is an absolute unit — it never changes based on context, which makes it predictable but inflexible for accessibility (it ignores a user's browser font-size preference). rem scales with the root <html> font size, making it the standard choice for accessible, consistently-scaling typography and spacing. em scales with the parent element's font size instead, which is powerful for component-relative sizing but can compound unexpectedly when nested — a common source of "why is this text huge" bugs. pt is mostly a print-context holdover; on screens, 1pt equals exactly 4/3 px per the CSS specification's 96dpi reference.
Frequently asked questions
Why do rem and em conversions depend on a base font size?
rem is always relative to the root (html) element's font size, while em is relative to the current element's font size — both are proportional units, so converting them to a fixed unit like px requires knowing that base size.