The amount of power drawn by a household appliance is given in watts. Here's how to calculate wattage.

### You will need

- Appliance
- Mathematical formulas

Step 1 Understand the definition Know that 1 watt is the amount of power produced by a current of 1 ampere across a potential difference of 1 volt.

**Quick Tip:**

Equivalently 1 watt is the amount of work done at the rate of one joule per second.

Step 2 Understand appliances Understand that the wattage listed on an appliance is the maximum power it draws. Because many appliances have a range of settings, the actual amount of power consumed at any given time depends on the setting used.

Step 3 Use a formula Consider using a formula to estimate wattage. To do this you will need to know the current draw, the voltage used by the appliance, and/or the resistance of the appliance.

Step 4 Use voltage and current Calculate the wattage from the product of voltage and the current for the appliance. Voltage is measured in volts and current in amperes (or amps).

**Quick Tip:**

If an appliance is rated at 5 amps and 120 volts, the wattage is 600 watts (5 amps times 120 volts, which equals 600 watts).

Step 5 Use current and resistance Obtain the wattage as the product of the square of current times the resistance. Resistance is measured in ohms.

Step 6 Use voltage and resistance Calculate the wattage from the quotient of the square of voltage divided by resistance.

** Did You Know:**

James Watt was an 18th-century mechanical engineer who made important contributions to improvements of the steam engine.