How much amoxicillin do i give my 40 pound dog?

Never never give medication to your dog at home without a Veterinarian being involved. You could cause much more harm than good and even possibly death. Your dog should be examined by your Veterinarian first. The Vet will prescribe the correct antibiotic, if needed, and the correct dosage for the condition the Vet is treating your dog for. Why on earth would you want to give amoxicillin to your dog without having him or her checked out by your Vet first?? Take your dog to your Vet.