All chimes are measured by the same standard among all manufacturers: the overall, complete height of the wind chime. This is from the very top of the hanging ring (or knot of strings in the Gentle Spirits chimes) to the bottom of the wind sail.
You can also find dimensions for each chime on the any chime page on the website. Look to the left under the picture of the chime and you'll find overall measurement, longest tube, tuning, etc.
The parts of a chime are labeled in the picture below. Of course, feel free to call us if you have any questions!