FIDDLE, now the whole thing will scale when you change the font-size
CSS
.icon_centering {
font-size: 5.5em;
line-height:2.5em;
height:2em;
width:2em;
vertical-align:middle;
overflow:hidden;
color: #FFF;
background: #428bca;
border-radius: 9999em;
display: inline-block;
text-align: center;
}