How many amps a hair dryer will use does vary from one model to the next. You should be able to locate the number of amps on the nameplate or on the box that the hair dryer came in. To determine amps you would simply take the watts and divide it by the volts. Most volts in the United States are between 110 and 120. Other countries outside of North America and Japan use 240 volts. The actual voltage coming out of your electrical socket can vary depending on the conditions at the power plant and in your home.