Kilowatts is a measure of energy conversion. One watt is equal to roughly one Joule of energy per second, while amps (amperage) are a measure of how much electricity ("current") is passing a specific point at a certain time. Kilowatt measures energy conversion in thousands of watts. Measuring the approximate kilowatt usage of an electrical system is beneficial when attempting to ascertain the energy usage of the household or whether or not an appliance is sustainable on a specific circuit.
Ascertain the amperage and voltage of the specific electrical system you wish to calculate kilowatt for. Check the manufacturer's documentation or the electrical label attached to the appliance itself for this information.
Multiply the amperage times the voltage.
Divide the product obtained by 1,000. For example, 120 volts times 10 amps equals 1,200 Watts. 1,200 divided by 1,000 equals 1.2kW.