<div class="box"> </div> <p>contentWidth = width</p> <div class="border-box"> </div> <p>contentWidth = width - (border-left + padding-left + padding-right + border-right)</p>
.box { box-sizing: content-box; width: 100px; height: 100px; background-color: #eee; border: 5px solid red; padding: 5px 10px 15px 20px; margin: 10px; } .border-box { box-sizing: border-box; width: 100px; height: 100px; background-color: #eee; border: 5px solid red; padding: 5px 10px 15px 20px; margin: 10px; }