Benadryl Tablets According to the Merck Veterinary Manual, the standard dose for Benadryl is 2-4 milligrams per kilogram of body weight, or 0.9-1.8 milligrams (mg) of Benadryl per pound. Therefore, a simple and practical dose is 1 mg of Benadryl per pound of your dog's weight, given 2-3 times a day.