The watt (W) is a convenience unit to describe the amount of work that current can do, as a factor of voltage and amperage, and is defined as:

Watts = Volts * Amps

Common Wattages

Electrical Current Voltage Amperage Wattage
Hair Dryer 117V 12A 1,404W
60 Watt Incandescent Light Bulb 117V ~0.5A ~60W
iPad/Tablet Charger 5V ~2A 10W
Netduino 5V 40mA 0.2W