If you going to use about 16 feet, you multiply 4.4 by 16, and you get 70.4 watts. 3. Divide the total wattage computed on the previous step by 12 to get the total amps or current. So, it would be 70.4 watts divided by 12, you get 5.87 amps. 4. Refer to the chart below to find the right wire gauge.