Since a Shih-Poo is a mix of these two breeds, their weight can vary quite a bit. Generally speaking, Shih-Poos weigh between 10 and 30 pounds when fully grown.
Of course, every dog is unique, and there will always be some variation in weight even within the same breed. So if you're curious about the ideal weight for your Shih-Poo, talk to your veterinarian.