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# How to Calculate Watts

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

### Instructions

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

### You Will Need

- Appliance
- Mathematical formulas