The simplest conversion formula to convert watts to amps is based on the formula for amps, which is power (in Watts) divided by Volts. This is written as I(Amps) = P(Watts) / V(Volts). By simply rearranging this formula, it is easy to convert amps to watts and vice versa.
This is the simplest formula involving amp and watt calculation. There are several more complicated formulae for AC single phase watts-to-amps calculation, AC three phase watts-to-amps calculation and amps calculation with line-to-line voltage. These formulae involve more complex equations and a greater understanding of physics and are specific to those situations.