Yes, 3Kg is over 6 and a half pounds - as you discovered a bit too much 
Your pigs should always look 'lean' as opposed to fat. If you can feel the backbone clearly, they're too skinny, but if you can't feel any ribs they're too fat 
But it's not just the quantity of feeding you've got to consider. Look at the size of area they're in, if it's small and they're not excercising they'll get even fatter than they would in a bigger area. You've also got to look at the ratio of feedstuffs - purely pig nuts ? barley & grain ? any part of the diet made up by fruit/veg/forage ? It's more complicated than just giving x amount per pig per day - every pig and every situation is different.
Hope that helps Pete ?
Karen 
Thanks for all the replies, I understand what you say insofar as the ground which ours have grass on tap at this point in time and we feed a mix of nuts (which i will be getting out of the way of due to imput chemicals,but story for another time) and rolled barley plus whatever comes out of the garden and some throw away carrotts etc. The bigger of the 3 is a proper "HOG" and she will stand out in the pissing rain to finish where the other two may come back later.
I can't stop her lust for food but also know that they are healthy. Credit to this site for my knowledge to a point and the ratio i feed is what it is meant to be ,but if a fatty wants it she has more weight to throw about to get what she wants....women ey lol.
off topic a bit,we just picked up another 3 weaners today (2landrace x york and one tammy x landrace). Interesting for them to meet the new neighbours and they want to sleep in thier hut but that's not happening.
Pigs are fecking addictive and we love them here.