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Hi! He has got a good weight. Weight charts for guinea pigs are an exercise in futility because the weight range is so large. You can check whether you guinea pig is a good weight for its size by feeling the 'heft' around its rib cage. You should be able to just about feel the ribs. They should not stand out singly and they also should not be covered in a layer of fat.
More information in this guide here: The Importance Of Weighing - Ideal Weight / Overweight / Underweight