What's the difference between HTML's and CSS's width attribute?

HTML vs. CSS Width: Understanding the Core Differences

Explore the fundamental distinctions between HTML's width attribute and CSS's width property, and learn how they impact layout and responsiveness in web development.

When styling web pages, developers often encounter width in both HTML attributes and CSS properties. While both seemingly control an element's horizontal dimension, their origins, application, and behavior are distinctly different. Understanding these differences is crucial for effective and maintainable web design, especially in the era of responsive layouts.

HTML's width Attribute: A Legacy Approach

The width attribute in HTML is an older method primarily used for specific elements like <img>, <table>, <canvas>, and <video>. It's a direct attribute on the HTML tag itself, specifying the intrinsic width of the element in pixels or, for tables, sometimes as a percentage. Its use is largely deprecated for layout control in favor of CSS, as it offers limited flexibility and poor separation of concerns.

<img src="image.jpg" width="300" alt="Example Image">

<table width="50%">
  <tr>
    <td>Table Content</td>
  </tr>
</table>

Examples of HTML width attribute usage

CSS's width Property: The Modern Standard

The CSS width property is the modern, flexible, and powerful way to control the horizontal dimension of almost any HTML element. It's part of the CSS Box Model and can accept various units (pixels, percentages, ems, rems, viewport units, etc.), allowing for highly responsive and adaptive designs. CSS width can be applied via inline styles, internal stylesheets, or external stylesheets, promoting a clear separation of structure (HTML) and presentation (CSS).

/* Using pixels */
.container {
  width: 600px;
}

/* Using percentages for responsiveness */
.responsive-box {
  width: 80%;
  max-width: 1200px; /* Prevents it from getting too wide */
}

/* Using viewport units */
.full-width {
  width: 100vw; /* 100% of viewport width */
}

Examples of CSS width property usage

flowchart TD
    A[HTML `width` Attribute] --> B{Applies to specific elements: `<img>`, `<table>`, etc.}
    B --> C[Directly on HTML tag]
    C --> D[Limited units: pixels, percentages (for tables)]
    D --> E[Primarily for intrinsic size, not layout]
    E --> F["Less flexible, not recommended for modern layout"]

    G[CSS `width` Property] --> H{Applies to almost all block-level elements}
    H --> I[Via stylesheets (inline, internal, external)]
    I --> J[Wide range of units: px, %, em, rem, vw, vh, etc.]
    J --> K[Fundamental for layout and responsiveness]
    K --> L["Highly flexible, standard for modern web design"]

    F --- M[Difference]
    L --- M

Comparison of HTML width attribute and CSS width property

Interaction and Precedence

When both an HTML width attribute and a CSS width property are applied to the same element, CSS generally takes precedence due to the cascading nature of stylesheets. However, the exact behavior can sometimes be nuanced, especially with older HTML elements or when using !important in CSS. For consistent and predictable results, it's best to exclusively use CSS for layout dimensions.