At 115 volts of current, 115 watts is equal to one amp, but the number of watts to equal an amp varies based on the current. If using a 12-volt battery to power the circuit, 12 watts is equal to one amp.
The formula for electricity is I=P/V, where I is the current in amps, P is the power in watts and V is the voltage of the circuit. Increasing the voltage in a circuit decreases the number of amps required, thus operating a 115-watt load at 230 volts requires only half the current. This decrease in demand for current increases the capacity of the circuit.