Edit in JSFiddle

<div class="btn">
    <a href="#" class="btnInner">1行ボタン</a>
</div>
<div class="btn">
    <a href="#" class="btnInner">2行<br>ボタン</a>
</div>
.btn {
    display: inline-block;
    margin: 0 5px 0 0;
}
.btnInner {
    display: table-cell;
    width: 200px;
    height: 100px;
    background: #000;
    color: #ccc;
    text-align: center;
    vertical-align: middle;
}