.block {
  background: #666;
  width: 100px;
  height: 100px;
  transition: all .15s linear;
}

var size = 0;

$('button').on('click', function() {
  size += 5;
  var square = (100 + size);
  $('.block').css({
    width: square + 'px',
    height: square + 'px'
  }).text(square + 'X' + square);
});