Suppose we have a 50x100
Since jQuery is an old library, it used some different combinations (of
offsetWidth/offsetHeight (and also
node.style)) over the times.
So, without knowing your used version of jQuery, it's hard to say what it does internally.
getBoundingClientRect gives you the actual dimensions of transformed elements.
Here's a small test case: https://jsfiddle.net/bxe1ve9q
I would bet that using
offsetWidth/offsetHeight should give the correct values.