<!DOCTYPE HTML> <meta charset=utf-8> <title>Bug 520992</title> <style> #borderBox { background:gold; height:100px; box-sizing:border-box; border: 20px solid gold; } </style> <div id="borderBox"></div> <p id="heightWidth1"></p> <script> var divs = document.getElementsByTagName("div"); var textEle1 = document.getElementById("heightWidth1"); textEle1.innerHTML += "height = " + getComputedStyle(divs[0]).height; textEle1.innerHTML += ", width = " + getComputedStyle(divs[0]).width; </script>