Penicillin is often prescribed for dogs in veterinary medicine. Of course, without a real life relationship, no one out here will be able to give you a dose of Amoxicillin for your dog.
That being said, if you go to this website: http://www.terrierman.com/antibiotics.htm , you will find the information you're looking for.
If you are giving your dog antibiotics for some kind of infection, it's always best to consult with your vet, just in case the infection requires a specific type of medication rather than a general one.
I hope this helps.