px, em, and ex in Font Size: Which Unit Should You Choose?

px, em, and ex in Font Size: Understanding the Differences

In CSS, we have three primary units for defining font size: px, em, and ex. Each has distinct characteristics and usage cases.

px

Px, short for "pixels," is an absolute unit that specifies the font size in pixels on the viewing device. It is precise and device-dependent, meaning the size will vary based on the screen resolution.

em

Em is a relative unit that refers to the current font size. By default, the font size in em is equal to the font size in pixels. However, it can be changed using the font-size property. When defining font size in CSS with em, you are instructing the browser to use a font size relative to the inherited font size.

ex

Ex is similar to em, but instead of referring to the font size, it refers to the x-height of the font. The x-height is the height of the lowercase letter "x." It is a unit that is primarily utilized in typography to calculate the spacing and proportions of the font.

When to Use Em and Px

• Use em when you want the font size to scale proportionally with the base font size. This is useful for creating flexible and responsive layouts where the font size can adapt to different devices and screen sizes.
• Use px when you want the font size to be precise and consistent across all devices. This is especially important for headlines, logos, and other elements where specific font sizes are desired.

Note: In CSS, it is generally recommended to use em instead of pt (points) for defining font size. Pt is a unit that has historical significance but is often less consistent across different devices and browsers.

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