The amount of chocolate that can kill a dog depends on the dog's weight and the type of chocolate, as darker chocolates contain more toxic substances (theobromine and caffeine) than milk chocolate.

• For milk chocolate, about 1 ounce per pound of a dog's body weight can be lethal. For example, a 3-pound dog could be fatally poisoned by just one standard 1.55-ounce Hershey’s Milk Chocolate bar

• For unsweetened baking (dark) chocolate, as little as 0.1 ounces per pound of body weight may be lethal, making it much more dangerous than milk chocolate

• Another source cites potentially fatal doses as approximately 0.5 ounces per pound for dark baking chocolate and 3 ounces per pound for milk chocolate , meaning a 10-pound dog could be fatally poisoned by 5 ounces of dark baking chocolate or 30 ounces of milk chocolate

• Toxicity symptoms can start at lower doses, and doses above about 55 mg of theobromine per kilogram of body weight may be fatal

In practical terms, even small amounts of chocolate can be dangerous, especially for small dogs or when the chocolate is dark or baking chocolate. Immediate veterinary attention is recommended if a dog consumes any amount of chocolate

Summary:

• Milk chocolate lethal dose: ~1 oz per pound of dog weight
• Dark/baking chocolate lethal dose: ~0.1 to 0.5 oz per pound of dog weight
• Toxic dose varies by chocolate type and dog size
• Symptoms can occur well before lethal dose
• Seek emergency vet care immediately if chocolate ingestion occurs

This means even a small amount of chocolate can be deadly for dogs, especially small breeds or with dark chocolate types.