Breakers are only rated to carry 80% of their rated load continuously. Some are made better than others and will do better but loading higher is probably against your local elect code. Also, consider what you are putting on that circuit. Any motors will draw more current shen they start up. Breakers are made to account for those short peaks but don't push the limit. When in doubt, check your local code. The formula stated earlier was correct but I think you will find your home voltage is running 120V or maybe a little higher. Using 115V won't hurt, it will only increase your safety margin.