Font Size Converter

A font size converter translates text size measurements between the various units used in web design, print design, and typography. Unlike length or weight conversions that have a single standard, font sizes are expressed in five primary units: pixels (px), points (pt), em, rem, and percentage (%). Each unit serves a different purpose and behaves differently depending on context. Pixels are absolute screen measurements, points are absolute print measurements, while em, rem, and percentage are relative units that depend on a base font size. Understanding these differences is essential for creating consistent, accessible, and responsive designs across devices.

The pixel (px) is the most commonly used unit for screen design. One pixel corresponds to one dot on a display screen, and pixel-based font sizes are predictable and consistent regardless of context. However, pixels do not scale with user preferences, which can create accessibility issues for users who need larger text. The point (pt) is the standard unit for print design, where 1 point equals exactly 1/72 of an inch. The conversion between pixels and points depends on screen resolution: at the standard web resolution of 96 DPI, 1 pt equals 1.333 px.

The relative units (em, rem, and percentage) are based on a configurable base font size, typically 16 pixels in web browsers. An em unit equals the current element's font size, while a rem unit equals the root element's font size (usually the HTML element's font size). This means that 1rem equals the base font size, regardless of where it appears in the document hierarchy. Percentage units work similarly: 100% equals the base font size. This converter also shows the viewport width equivalent (vw), which scales text relative to the browser window width.

Each unit converts to pixels using a different formula based on the base font size. All conversions pass through pixels as the intermediate unit.

Use this calculator to convert font sizes between pixels, points, em, rem, and percentage:

1. Enter the font size value: Type the numerical value into the input field.
2. Select the source unit: Choose the unit you are converting from: px, pt, em, rem, or %.
3. Set the base font size: Enter the base font size in pixels. The default is 16 px, which is the standard browser default. Change this if your project uses a different base size.
4. Read all results: The calculator shows the font size converted to all six units simultaneously: px, pt, em, rem, %, and vw (based on a 1920px viewport width).
5. Preview the text: A preview pane displays sample text rendered at the computed pixel size so you can visually assess the result.
6. Try common sizes: Click any of the common font size presets (from 10px "Tiny" to 96px "Display") to quickly load and convert standard sizes.

The calculator outputs six equivalent font sizes:

• Pixels (px): The absolute screen measurement. This is the most common unit for web design and the value that browsers ultimately render on screen.
• Points (pt): The absolute print measurement. 1 pt = 1/72 inch. Points are used in print design and some desktop publishing applications.
• Em: A relative unit based on the current element's font size. 1em equals the inherited font size. Em compounds in nested elements, making it useful but potentially unpredictable.
• Rem: A relative unit based on the root element's font size. 1rem equals the base font size (typically 16px). Rem does not compound in nested elements, making it more predictable than em.
• Percentage (%): Works like em for font sizes. 100% equals the base font size. 50% is half the base size, 200% is double.
• Viewport Width (vw): Scales text relative to the browser window. 1vw equals 1% of the viewport width. Useful for fluid typography that scales with screen size.

The relationship between em and rem is that em is relative to the parent element while rem is always relative to the root. For elements at the top level of the document, em and rem produce the same result. For nested elements, em values compound while rem values remain constant.

Font size conversion is essential in responsive web design, where text must render legibly across devices ranging from small phones to large desktop monitors. Using relative units like rem and em allows text to scale automatically based on user preferences and browser settings, which is critical for accessibility. The Web Content Accessibility Guidelines (WCAG) recommend that users be able to resize text up to 200% without breaking the layout, and using relative units makes this possible.

In print design and publishing, points are the standard unit for body text and headings. A typical book body text size is 10-12 pt, while headlines range from 14-36 pt or larger. When translating a print design to the web, designers must convert point sizes to pixels or rem values. The standard conversion at 96 DPI is 1 pt = 1.333 px, but this changes at different screen resolutions.

In email design and newsletter creation, font size units matter because email clients render HTML differently. Most email clients support pixel-based font sizes reliably, but some older clients have issues with em and rem. Understanding how font sizes convert between units helps designers choose the right unit for maximum compatibility across email clients and devices.