he sounds a bit under weight - id be taking him to the vet.
We bought spud when he was 3 months old and he was 4 or 5 kilos (i think from memory)
Ive been reading about worms in dogs (because spud now has it) and extreme weight loss was a symptom.
As with humans, we all differ. Even so, that seems to be under what I would think to be the same as Danielle has said. I did the conversion on my last two pugs from being as old as what Tin Tin is. They were 4.5 to 5.3 kilos. The one I kept is now 17 months old and weights just under 10 kilos. Might be worth having Tin Tin checked out by a Vet just for your peace of mind.
"And now we have lost sweet Tin Tin, beloved by Puggirl. Pugs come into our lives to brighten them, and that is exactly what they do. Sweet Tin Tin, please find our puggies that have gone on before us and tell them we still remember…"