CSS Units Explained: PX vs REM vs EM vs VW (With Free Converter Tools)
If you've ever gotten confused about when to use px vs rem vs em in CSS, you're not alone. This is one of the most common sources of confusion for developers at every level. The Quick Answer px → Fixed size, doesn't scale. Use for borders, box shadows. rem → Relative to root font size (16px default). Use for font sizes, spacing. em → Relative to parent font size. Use with caution, compounds with nesting. vw/vh → Relative to viewport size. Use for full-screen layouts, fluid typography. Deep Dive: When Each Unit Makes Sense PX - Use for Fixed Elements border : 1 px solid #ccc ; box-shadow : 0 2 px 4 px rgba ( 0 , 0 , 0 , 0 . 1 ); Never use px for font sizes - it overrides user browser font size preferences, breaking accessibility. REM - Your Default for Most Things REM is relative to the <html> element font size. Browser default is 16px. /* 16px → 1rem */ /* 24px → 1.5rem */ /* 14px → 0.875rem */ font-size : 1 rem ; /* 16px */ padding : 1 . 5 rem ; /* 24px */ margin-bottom : 2 rem ; /* 3
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