Liquid Benadryl dose in ml = Weight of cat / (Concentration of liquid) Say your cat weighs 12 pounds. Liquid Benadryl = 12 / (12.5 mg / 5 ml) Liquid Benadryl = 12 / 2.5 mg/ml Liquid Benadryl = 4.8 ml Is 25 mg Benadryl safe for a cat? The vets recommend 1 mg of Benadryl per...