The default value of font size in most browsers is 16px. If we do not specify any font size for the text or its parent element does not have a specific font size, it takes the default font size of that browser which is usually 16px. Thus by default, 1em corresponds to a font size of 16px and 2em to a font size of 32px.
Let's understand it with the help of an example, taking the font size of the web page as 16px.