How to get element width/height with margin, padding, border in Native JavaScript (no jQuery)

If you’re only dealing with pixel values for the margin, padding and border properties, you can do the following:

// we're assuming a reference to your element in a variable called 'element'
var style = element.currentStyle || window.getComputedStyle(element),
    width = element.offsetWidth, // or use style.width
    margin = parseFloat(style.marginLeft) + parseFloat(style.marginRight),
    padding = parseFloat(style.paddingLeft) + parseFloat(style.paddingRight),
    border = parseFloat(style.borderLeftWidth) + parseFloat(style.borderRightWidth);

alert(width + margin - padding + border);

If you’re dealing with other kinds of values (like ems, points or values like auto), I would like to refer you to this answer.