How much should a chihuahua dog weight?

That depends on your chi. Is it a showing chi? If it's being shown in dog shows it can weigh no more than 6 lbs. If it's not being shown, and is just a member of the family your vet can tell you what the right weight is for your chi. Some chi's weigh less, some more. Mine is a 4 year old deerhead and she has a steady weight of 10 lbs.