The border-width shorthand CSS property sets the width of an element's border.

Constituent properties

This property is a shorthand for the following CSS properties:


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

/* <length> values */border-width: 4px;
border-width: 1.2rem;
/* vertical | horizontal */
border-width: 2px 1.5em;

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

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

/* Global keywords */
border-width: inherit;
border-width: initial;
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).


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 A thin border
medium A medium border
thick A thick border

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

Initial value as each of the properties of the shorthand:
Applies to all elements. It also applies to ::first-letter.
Inherited no
Computed value as each of the properties of the shorthand:
Animation type as each of the properties of the shorthand:

Formal syntax


<line-width> = <length> | thin | medium | thick


A mix of values and lengths


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


#sval {
  border: ridge #ccc;
  border-width: 6px;
#bival {
  border: solid red;
  border-width: 2px 10px;
#treval {
  border: dotted orange;
  border-width: 0.3em 0 9px;
#fourval {
  border: solid lightgreen;
  border-width: thin medium thick 1em;
p {
  width: auto;
  margin: 0.25em;
  padding: 0.25em;



Specification Status Comment
CSS Backgrounds and Borders Module Level 3
The definition of 'border-width' in that specification.
Candidate Recommendation No direct change; the <length> CSS data type extension has an effect on this property.
CSS Level 2 (Revision 1)
The definition of 'border-width' in that specification.
Recommendation Added the constraint that values' meaning must be constant inside a document.
CSS Level 1
The definition of 'border-width' in that specification.
Recommendation Initial definition.

Browser compatibilityUpdate compatibility data on GitHub

Chrome Edge Firefox Internet Explorer Opera Safari
border-width 1 12 1 4 3.5 1
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
border-width 2 18 4 10.1 3 1.0

See also

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