Amps decide whether a circuit, breaker or extension cord can carry a load safely. Nameplates print watts far more often than amps, so converting between them is the first step in almost any wiring question.
Amps equal watts divided by volts. A 1,500 W appliance on a 120V circuit draws 12.5 amps; the same appliance on 240V draws half that, 6.25 amps, for the same power delivered.
Amp draw for every appliance
[hed_amp_index]The 80 percent rule
US electrical code treats any load running half an hour or longer as continuous, and continuous loads must not exceed 80 percent of a circuit breaker rating. A device drawing 12 amps continuously therefore needs at least a 15A breaker, even though 12 amps looks like it fits comfortably under 15. That headroom, not the raw draw, is what actually sizes a circuit.