When calling .height(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, a valid CSS measurement must be provided for the height (such as 100px, 50%, or auto).Note that in modern browsers, the CSS height property does not include padding, border, or margin.

The reason why the "viewable" word is specified, is because if the element's content is wider than the actual width of the element, this property will only return the width that is visible (See "More Examples"). The offsetWidth property returns the viewable width of an element in pixels, including padding, border and scrollbar, but not the margin.