It is always helpful aboard to know how to convert electric power in watts (W) to electric current in amps (A), here is an easy calculator :
Watts to amps (A) conversion calculator
Watts to amps (A) conversion calculator
Just remember PIE or P = IE, Then re-arrange to find the missing term.
Power (watts) = Current(amps) x Volts
or
Current(amps) = Power(watts) / Volts
or
Volts = Power(watts) / Current(amps)
Maybe I missed it in the nice calculator, but - another complication to remember:
If you're figuring amp draw from batteries when using a 120V device through an inverter, add 10-15% to your amp calculations for inverter inefficiencies.