Oh right, a bit more tricky then.
What I'd do if it were me is this:
Split the pack into 2 equal piles that fit equally into the same volume of the same container. so I know each is 500g.
Then I'd split one of those piles into 4 using the same process (volume of same container) so I know each is 125g.
Then I'd split one of those piles into 5 equal piles, using the same process so I know each is 25g.
Then I'd know I'm in the right ball park.
PS I take it you mean SN, not NS? Unless I'm missing some glossary.