Choose an Inverter or Inverter/Charger based on the devices it will power. If a device is not on the list, and is rated in amps, convert amps into watts by multiplying a device’s amps by its voltage. For example, a ¼" drill requires 2½ amps (2½ x 120 = 300 watts). Always choose an inverter with a rating greater than or equal to required wattage.