When Avie was 5months old, i want to say she weighed around 3lbs.. she is full grown now and weighs 6lbs.
Gemma is 5 months old and weighs 1.5 lbs. she is very little. but has a huge personality.
..like others said you can use the growth chart as a basis & it is a pretty accurate guide to go by.. but it really just depends on your baby! if you got her from a breeder who knows their 'lines'(parents, grandparents,etc), that can also help figure out the adult weight of your lil one.