There is not a set number, but you want to make sure you have enough to keep your dog entertained. The toys should be suitable for your dog's size and age and aligned with their interests. For example, if your dog loves to play fetch, you should keep a few balls on hand at a time, and if your dog loves to play hide-and-seek, you'll want to mix things up to keep them guessing. Once a toy rips or breaks, it's important to take it away to prevent your dog from ingesting any of the material inside or pieces that come loose.