The standard mains voltage used in the United States is approximately 110 to 120 volts, according to Georgia State University's physics department. Depending on the power load, it can vary between these two measurements.
It is important to remember that the 120-volt measurement is an approximation rather than a set measurement. Alternating current circuits have voltages that are constantly switching polarities and varying in measurement. The 120-volt measurement is effectively an average known as the root mean square. In fact, it can get as high as 170 volts AC on an average household circuit.
Certain appliances in a home, such as a washer or dryer, require more power and thus their own circuit. These circuits can reach 240 volts AC.