How much should my Guinea pig Weigh?

It varies from pig to pig. My girls weigh 30-35oz. I used to have a girl that was 38oz. All are/were healthy weights. My 35oz pig used to be 40oz and she was overweight at 40oz. I also used to have a 45oz pig and she was overweight. If you have to dig to feel her ribs she's overweight. You should be able to feel ribs with slight pressure. A dewlap/double chin can be (but isn't always) a sign she's overweight. My overweight girls had dewlaps while my girls who are/were at a good weight did/do not. If her stomach touches the ground when she walks she's overweight. If she has a heavy pear shape she's probably overweight. You can always take her to a cavy savvy vet and see what they think.

You want to feed a proper diet and give them a proper sized cage to prevent obesity or to help her lose weight if she is overweight. Guinea pigs need unlimited hay, a cup of veggies per pig and only 2 tablespoons of good quality pellets (guinea pigs under 6 months need unlimited pellets). Minimum cage size is 8 square feet but bigger is better. Even when I had my overweight girls in a 20 square foot cage they maintained their weight. I expanded a few times and each time I did they lost a little weight. Eventually their cage was 60 square feet for 4 pigs and that's when they got down to a healthy weight. So make the cage as big as possible.

females adult piggies should weigh about 700 to 900 grams for adult males it should be from about 900 to 1200 but all guinea pigs are different if you are really worried about your bundle f cuteness you should take her to a vet