CSS3 calc and attr usage

width: calc(2*20%); content: attr(data-width);

HTML

<div class='test' data-name=" - CONTENT" data-width="400">teste</div>

CSS

.test {
    display: inline-block;
    background-color: gray;
    width: calc(attr(data-width)*1px);
}

.test:after {
    content: attr(data-width);
}