The ideal weight for an Australian (American/Pet type) budgie is often between 25 -39+ grams, averaging 35, based on body size.
English budgies average is around 45 grams with it ranging from 42 grams to 60 grams depending on body size.
However, there is a gray area where bone structure can qualify.
When in doubt check the keel bone in relation to the breast muscle. An overweight budgie, for the bone structure may not be a good flyer.
Watch your bird fly around the room and then roost. If the budgie exhibits heavy breathing, then the weight is a little heavy.