Create block level buttons that span the full width of a parent- by adding .btn-block.
<!DOCTYPE HTML>
<html>
<head>
<link href="http://java2s.com/style/bootstrap.min.css" rel="stylesheet">
</head><!--from w ww .j av a 2s.c o m-->
<body style='margin:20px;'>
<button type="button" class="btn btn-primary btn-lg btn-block">Block level button</button>
<button type="button" class="btn btn-default btn-lg btn-block">Block level button</button>
</body>
</html>