Although they vary slightly as to how they retrieve a height value, i.e some would calculate the whole element including padding, margin, scrollbar, etc and others would just calculate the element in its raw form.
You can try these ones:
javascript:
var myDiv = document.getElementById("myDiv");
myDiv.clientHeight;
myDiv.scrollHeight;
myDiv.offsetHeight;
or in jquery:
$("#myDiv").height();
$("#myDiv").innerHeight();
$("#myDiv").outerHeight();