I don't own any picotin, but I find this measurements from a Japanese booklet. Hope this will help.
GM: H30xW30xD20
MM:H22xW24xD18
PM: H17XW20XD14
It also comes in bi-color with one half of the bag one colour and the other half of the bag another.
Thanks! Just 2 more questions - is it in inches? and what does GM, MM, PM stand for?