The short answer is none. Giving your dog activated charcoal without the advisement, supervision, or advice from your veterinarian can cause harm to your dog. According to dvm360.com: The recommended dose of activated charcoal in small animals is 1 to 5 g/kg of body weight orally. Without knowing exactly what your dog is eating, or how much it’s already consumed through food, it wouldn’t be difficult to give your dog too much. Again, let the vet help you to figure out what’s best.