A gemstone's crown height varies significantly depending on the cutting style (see images at left). Measuring from girdle to culet is typically one of the most important dimensions for determining whether a gem will fit in a particular setting.
This measurement is difficult to do and so the measurement can differ by .2-.3 mm from the true pavilion depth. We do our best and it is usually quite close, but this measurement is somewhat imprecise.
There are some gems that have only the total depth and NOT the pavilion depth listed so please pay close attention to the details of the gem you are looking at.