.width()
.width() Returns: Integer
Description: Get the current computed width for the first element in the set of matched elements.
version added: 1.0.width()
The difference between .css(width) and .width() is that the latter returns a unit-less pixel value (for example, 400) while the former returns a value with units intact (for example, 400px). The .width() method is recommended when an element's width needs to be used in a mathematical calculation.

This method is also able to find the width of the window and document.
$(window).width(); // returns width of browser viewport $(document).width(); // returns width of HTML document
Example:
Show various widths. Note the values are from the iframe so might be smaller than you expected. The yellow highlight shows the iframe body.
<!DOCTYPE html>
<html>
<head>
<style>
body { background:yellow; }
button { font-size:12px; margin:2px; }
p { width:150px; border:1px red solid; }
div { color:red; font-weight:bold; }
</style>
<script src="http://code.jquery.com/jquery-latest.min.js"></script>
</head>
<body>
<button id="getp">Get Paragraph Width</button>
<button id="getd">Get Document Width</button>
<button id="getw">Get Window Width</button>
<div> </div>
<p>
Sample paragraph to test width
</p>
<script>
function showWidth(ele, w) {
$("div").text("The width for the " + ele +
" is " + w + "px.");
}
$("#getp").click(function () {
showWidth("paragraph", $("p").width());
});
$("#getd").click(function () {
showWidth("document", $(document).width());
});
$("#getw").click(function () {
showWidth("window", $(window).width());
});
</script>
</body>
</html>
Demo:
.width( value ) Returns: jQuery
Description: Set the CSS width of each element in the set of matched elements.
-
version added: 1.0.width( value )
valueAn integer representing the number of pixels, or an integer along with an optional unit of measure appended (as a string).
-
version added: 1.4.1.width( function(index, width) )
function(index, width)A function returning the width to set. Receives the index position of the element in the set and the old width as arguments.
When calling .width('value'), the value can be either a string (number and unit) or a number. If only a number is provided for the value, jQuery assumes a pixel unit. If a string is provided, however, any valid CSS measurement may be used for the width (such as 100px, 50%, or auto). Note that in modern browsers, the CSS width property does not include padding, border, or margin.
If no explicit unit was specified (like 'em' or '%') then "px" is concatenated to the value.
Example:
To set the width of each div on click to 30px plus a color change.
<!DOCTYPE html>
<html>
<head>
<style>
div { width:70px; height:50px; float:left; margin:5px;
background:red; cursor:pointer; }
</style>
<script src="http://code.jquery.com/jquery-latest.min.js"></script>
</head>
<body>
<div></div>
<div>d</div>
<div>d</div>
<div>d</div>
<div>d</div>
<script>
$("div").one('click', function () {
$(this).width(30)
.css({cursor:"auto", "background-color":"blue"});
});
</script>
</body>
</html>

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