I don't know how heavy my third child is, he's five months. Whilst the weight charts are a useful indication of growth, they can also cause parents to obsess over which percentile there child is on. My take on it is, if your child is thriving and continues on roughly the same centile then everything is OK.
But I have heard some parents whose child has been steadily weighed on one centile, trying to get them heavier as they see this to be more healthy. The size of your baby is not only determined by how much you feed them, but also by their genetics, if the baby's parents are small framed, light people it's unlikely that they are going to be cruising around the 95th percentile.
Jools