Measuring a gaiwan
My gaiwan holds 150 ml if I fill it to the very top. But if I brew 5 grams of leaf and pour an infusion, that infusion is 100 ml.
So do I have a 150 ml gaiwan or a 100 ml?
Usually go off initial vessel size before tea.
The amount you get after steeping will very much vary by time and leaf. With a ball oolong I will get less and less tea as the session goes on as the leaf expands and takes up room.
The measure is also inaccurate as people use different amounts of tea. If I was using a 150ml gaiwan I would be using 10g of tea at least, around 7.5 for greens.
i would say you have a gaiwan of 150 mL volume of leaf and water. :-P
Indeed, at Wan Ling Tea House we always measure the empty gaiwan. As Oolong Owl said there are just too many variables otherwise.
Typically we usually give figures a little less than to the rim as obviously if you put the lid on you displace some liquid.
Similar process is done with teapots, usually we fill to the limit when you fit the lid.