Font Size Conversion Calculator
The Font Size Conversion Calculator is a free online tool for converting font sizes between pixels (px), root ems (rem), ems (em), and percent (%) values. Set the base font size, enter a font size and unit, and instantly view the equivalent values.
The default base font size is 16px, which is the common default used by web browsers. Change the base size to match your webpage or project, and use the live preview to compare the selected font size with the base font size.
Font Size Preview
Base Font Size
Font Size
Converted Values
| PX | 24px | |
| REM | 1.5rem | |
| EM | 1.5em | |
| Percent | 150% |
CSS Font Size Units
CSS provides several units for defining font sizes. Pixels use a fixed CSS length, while rem, em, and percentage values calculate a size relative to another font size. This calculator uses the selected base font size to compare these units directly.
Pixels (px)
Pixels are CSS absolute length units commonly used for precise sizing. A value such as 16px specifies the font size directly rather than calculating it as a percentage or multiple of another font size.
Root Ems (rem)
The rem unit is relative to the font size of the document's root <html> element. If the root font size is 16px, then 1rem equals 16px, 1.5rem equals 24px, and 2rem equals 32px.
Ems (em)
The em unit is relative to the applicable font-size context. For the font-size property, an em value is calculated from the inherited font size of the element. This calculator uses the selected base font size as the reference so that em values can be compared directly with the other units.
Percent (%)
A percentage font size is calculated relative to the inherited font size. With a base size of 16px, 100% equals 16px, 150% equals 24px, and 200% equals 32px.
Base Font Size
The base font size provides the reference used by the calculator when converting relative units. The default is 16px, but it can be changed to match the font-size settings used by a particular webpage or project.
Font Size Preview
The live preview displays the base font size and converted font size using the same sample text. Comparing the two examples makes it easier to see how changes in relative or absolute font sizes affect the visual size of text.