EmperioAf, а начиная с ie9, через transform
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style>
div{
width: 50px;
height: 50px;
background: #123;
}
div:hover{
transform:scale(1.25);
}
</style>
</head>
<body>
<div></div>
</body>
</html>