Determining the True Height of Letters in CSS Font-Size
When setting a font size in CSS, it's important to understand what its true height represents. Contrary to what you might think, the font size does not directly correspond to the pixel height of letters. Instead, it refers to a concept called the "em."
Historical Origins of "Em"
The "em" originated in the days of metal movable type printing. It referred to the square block that contained each letter, typically based on the height of the capital letter "M." With the advent of digital fonts, this physical limitation no longer applies.
Standards and Unit Conversion
In modern font technology, the "em" remains an imaginary boundary in software. It is generally set to 1000 units in OpenType fonts and 1024 or 2048 units in TrueType fonts. To define a font size accurately, use the "em" unit, as it represents the distance between the baseline and the mean line of the font, not the pixel height.
Conversion between different typographic units and screen resolutions can be complex. However, it's important to note that 1 point (Truchet) equals approximately 0.35 mm, and 1 pixel (PX) is a single "dot" on a screen, which varies depending on the screen resolution.
Inconsistencies in Actual Size
Despite the existence of standards, the actual height of glyphs in a given font can vary significantly depending on:
- How the font developer designed the glyphs
- The browser's rendering of the characters
- The resolution and pixel density of the screen
For example, the Zapfino script font created by Apple was originally sized relative to the largest capitals in the font. However, the lowercase letters appeared small, so the font was later revised to make a given point size approximately 4 times larger than other fonts.
Practical Implications
Understanding the true nature of font size in CSS is crucial for ensuring consistent and accurate typography in digital design. It's essential to consider the font's metrics, browser compatibility, and screen resolution when specifying font sizes to achieve the desired visual impact.
The above is the detailed content of What Does Font-Size Actually Measure in CSS?. For more information, please follow other related articles on the PHP Chinese website!

In this post, Blackle Mori shows you a few of the hacks found while trying to push the limits of Cohost’s HTML support. Use these if you dare, lest you too get labelled a CSS criminal.

Custom cursors with CSS are great, but we can take things to the next level with JavaScript. Using JavaScript, we can transition between cursor states, place dynamic text within the cursor, apply complex animations, and apply filters.

Interactive CSS animations with elements ricocheting off each other seem more plausible in 2025. While it’s unnecessary to implement Pong in CSS, the increasing flexibility and power of CSS reinforce Lee's suspicion that one day it will be a

Tips and tricks on utilizing the CSS backdrop-filter property to style user interfaces. You’ll learn how to layer backdrop filters among multiple elements, and integrate them with other CSS graphical effects to create elaborate designs.

Well, it turns out that SVG's built-in animation features were never deprecated as planned. Sure, CSS and JavaScript are more than capable of carrying the load, but it's good to know that SMIL is not dead in the water as previously

Yay, let's jump for text-wrap: pretty landing in Safari Technology Preview! But beware that it's different from how it works in Chromium browsers.

This CSS-Tricks update highlights significant progress in the Almanac, recent podcast appearances, a new CSS counters guide, and the addition of several new authors contributing valuable content.

Most of the time, people showcase Tailwind's @apply feature with one of Tailwind's single-property utilities (which changes a single CSS declaration). When showcased this way, @apply doesn't sound promising at all. So obvio


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Dreamweaver Mac version
Visual web development tools

SecLists
SecLists is the ultimate security tester's companion. It is a collection of various types of lists that are frequently used during security assessments, all in one place. SecLists helps make security testing more efficient and productive by conveniently providing all the lists a security tester might need. List types include usernames, passwords, URLs, fuzzing payloads, sensitive data patterns, web shells, and more. The tester can simply pull this repository onto a new test machine and he will have access to every type of list he needs.

mPDF
mPDF is a PHP library that can generate PDF files from UTF-8 encoded HTML. The original author, Ian Back, wrote mPDF to output PDF files "on the fly" from his website and handle different languages. It is slower than original scripts like HTML2FPDF and produces larger files when using Unicode fonts, but supports CSS styles etc. and has a lot of enhancements. Supports almost all languages, including RTL (Arabic and Hebrew) and CJK (Chinese, Japanese and Korean). Supports nested block-level elements (such as P, DIV),

SublimeText3 English version
Recommended: Win version, supports code prompts!

VSCode Windows 64-bit Download
A free and powerful IDE editor launched by Microsoft
