On the back of your appliance, you will find a label describing the power requirements. You should see a label describing the Wattage (W), Voltage (V) or the Amperage (A) of the appliance. Once noted, choose a power inverter which can handle a higher amount of wattage then your device is rated at. Certain devices which are motor based may require additional power to start up then indicated (know as Surge), in this case always add an extra 20% to the power requirements of your device.