border-width - CSS

Try it

border-width: thick;

border-width: 1em;

border-width: 4px 1.25em;

border-width: 2ex 1.25ex 0.5ex;

border-width: 0 4px 8px 12px;

<section class="default-example" id="default-example">
  <div class="transition-all" id="example-element">
    This is a box with a border around it.
  </div>
</section>

#example-element {
  background-color: palegreen;
  color: black;
  border: 0 solid crimson;
  padding: 0.75em;
  width: 80%;
  height: 100px;
}

Constituent properties

This property is a shorthand for the following CSS properties:

Syntax

css

/* Keyword values */
border-width: thin;
border-width: medium;
border-width: thick;

/* <length> values */
border-width: 4px;
border-width: 1.2rem;

/* top and bottom | left and right */
border-width: 2px 1.5em;

/* top | left and right | bottom */
border-width: 1px 2em 1.5cm;

/* top | right | bottom | left */
border-width: 1px 2em 0 4rem;

/* Global values */
border-width: inherit;
border-width: initial;
border-width: revert;
border-width: revert-layer;
border-width: unset;

The border-width property may be specified using one, two, three, or four values.

When one value is specified, it applies the same width to all four sides.
When two values are specified, the first width applies to the top and bottom, the second to the left and right.
When three values are specified, the first width applies to the top, the second to the left and right, the third to the bottom.
When four values are specified, the widths apply to the top, right, bottom, and left in that order (clockwise).

Values

<line-width>

Defines the width of the border, either as an explicit nonnegative <length> or a keyword. If it's a keyword, it must be one of the following values:

thin
medium
thick

Note: Because the specification doesn't define the exact thickness denoted by each keyword, the precise result when using one of them is implementation-specific. Nevertheless, they always follow the pattern thin ≤ medium ≤ thick, and the values are constant within a single document.

Formal definition

`border-left-width`: a `border-top-width`: a length
`border-bottom-width`: `medium` Computed value	as each of the properties of the shorthand: `border-left-style` is `none` or `hidden` `border-top-style` is `none` or `hidden`

Formal syntax

border-width = 
  |
  thin            |
  thick

Examples

A mix of values and lengths

HTML

html

<p id="one-value">one value: 6px wide border on all 4 sides</p>
<p id="two-values">
  two different values: 2px wide top and bottom border, 10px wide right and left
  border
</p>
<p id="three-values">
  three different values: 0.3em top, 9px bottom, and zero width right and left
</p>
<p id="four-values">
  four different values: "thin" top, "medium" right, "thick" bottom, and 1em
  left
</p>

CSS

css

#one-value {
  border: ridge #cccccc;
  border-width: 6px;
}
#two-values {
  border: solid red;
  border-width: 2px 10px;
}
#three-values {
  border: dotted orange;
  border-width: 0.3em 0 9px;
}
#four-values {
  border: solid lightgreen;
  border-width: thin medium thick 1em;
}
p {
  width: auto;
  margin: 0.25em;
  padding: 0.25em;
}

Result

Specifications

Specification
CSS Backgrounds and Borders Module Level 3 # border-width

Browser compatibility

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This page was last modified on ⁨Nov 7, 2025⁩ by MDN contributors.

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