Relationship between font-size and width of container

Is font size based on width or height?
What does font size affect?
Which unit of measure is based upon the set font size of its parent container?
What is the rule for font size?

Is font size based on width or height?

A font is often measured in pt (points). Points dictate the height of the lettering. There are approximately 72 (72.272) points in one inch or 2.54 cm. For example, the font size 72 would be about one inch tall, and 36 would be about a half of an inch.

What does font size affect?

To understand what font size to use you need to understand your target audience, the message you are trying to communicate, and what you want them to do (amongst other things). Note: Font size impacts page experience metrics, page speed, accessibility and usability.

Which unit of measure is based upon the set font size of its parent container?

rem Unit. The rem unit, short for root em is a relative unit that'll always be based upon the font-size value of the root element, which is the <html> element.

What is the rule for font size?

There are no exact rules for font sizing, but there are some generally good practices to think about when designing for desktop: Body text - Font sizes should be around 16px to 18px for legibility (or 1.6rem to 1.8rem using our sizing rules mentioned above).