LOL, okay, if it's Penicillin G Procaine, then it's dosed at 15,000 IU per pound, given 1-2x day.
If your drug contains 300,000 IU per ml, then 1 ml of your penicillin treats 20 lb of dog.
Weigh your dog, do the math, and give the appropriate dose 1-2x/day based on the severity ... IFFFF penicillin is even called for. You haven't stated the problem your dog is having, so penicillin might not even work.
Jack