What’s the difference between px, em, rem, %, vw, and vh?


px, em, rem, %, vw, and vh are units of measurement used in web development and design to specify the size or dimensions of elements on a webpage. Each of these units has its own characteristics and use cases:

1. px (Pixels):
   • Pixels are a fixed unit of measurement.
   • 1px is equal to one screen pixel, and it’s not affected by the browser’s zoom settings.
   • Often used for precise control of element sizes, borders, and text.
   • Not responsive, so may not adapt well to different screen sizes or resolutions.
2. em:
   • em is a relative unit of measurement based on the font size of the parent element.
   • 1em is equal to the font size of the current element. For example, if the font size of the parent element is 16px, 1em is 16px.
   • Useful for creating responsive designs that scale with text size changes.
3. rem (Root em):
   • rem is similar to em, but it’s based on the root (HTML) element’s font size.
   • 1rem is equal to the font size of the root element, so it’s not affected by nesting.
   • Often used for creating scalable and consistent layouts across the entire webpage.
4. % (Percentage):
   • Percentages are relative to the size of the parent element or containing block.
   • For example, setting the width of an element to 50% means it will take up half of the width of its parent element.
   • Useful for creating responsive layouts that adapt to the size of their containers.
5. vw (Viewport Width):
   • vw is a unit that represents a percentage of the viewport width.
   • 1vw is equal to 1% of the width of the viewport (the visible area of the browser window).
   • Useful for creating responsive designs that adapt to the width of the user’s screen.
6. vh (Viewport Height):
   • vh is similar to vw, but it represents a percentage of the viewport height.
   • 1vh is equal to 1% of the height of the viewport.
   • Useful for creating responsive designs that adapt to the height of the user’s screen.

Choosing the right unit depends on the specific design and layout requirements of your website or web application. rem and % are often preferred for responsive design, while px is useful when precise control is needed. em can be handy for text sizing that adjusts with the user’s preferences, and vw and vh are great for adapting to different screen sizes.