<input type="checkbox" class="bLarger" name="checkBox">

<style type="text/css">
input.bLarger{width: 20px; height: 20px;}</style>

input[type=checkbox]
{
  /* Double-sized Checkboxes */
  -ms-transform: scale(2); /* IE */
  -moz-transform: scale(2); /* FF */
  -webkit-transform: scale(2); /* Safari and Chrome */
  -o-transform: scale(2); /* Opera */
  padding: 10px;
}