text: what is the formula for figuring out how many watts an appliance useses? i know it has something to do with the voltage and the amps but not sure the set up of the equation. the first part of the formula is knowing how many watts the appliance uses. the old standard light bulb is the easiest to find out. just look on the top of the incandescent bulb and it will say: 60, 75 or 100 watts. with appliances you may have to do an extra step. on the back or bottom of the appliance will be a label or plate with data on it. if the watts used are not shown, find how many amps the appliance uses. once you know the amps you can calculate the watts used.  the formula for finding out how many watts that are being used is: amps multiply volts equals watts