# Units: px, rem, em, % and Viewport Units

Every size in CSS needs a unit, and choosing the right one, px, rem, em, %, vw or vh, decides whether your page grows with the reader's text, fits its space and stays readable.

![Cheat sheet: Units: px, rem, em, % and Viewport Units](https://fsdtrainingmedia.blob.core.windows.net/public/images/2026/10/6a5bc68654c74382853f5775d33dac3b.webp)

- Category: CSS
- Level: Apprentice
- Tags: CSS, em unit, Maximum size, Percentage, Pixel, rem unit, Viewport, web-development
- Updated: November 1, 2026

Source: https://www.ask-codey.com/cheat-sheets/css-units-cheat-sheet