Power can be measured in kVA or kW. Power ratings on appliances can be expressed in either, but there is an important difference between the two. kVA is referred to as "apparent power," and kW as "real power." The two are equal when voltage and current are in phase, but when they are out of phase, as is often the case with alternating current, apparent power can be higher than the actual amount of real power available.

Ratings on electrical equipment can be expressed in kW or kVA, but when the voltage and current are out of phase these values will differ.

Step 1

Look up the "power factor" for the electrical appliance in question. It will be between zero and one (or zero and 100 percent). Some manufacturers will include this information in the operating manual shipped with the appliance. Others may simply claim the appliance is "power factor corrected." This means they have added corrective elements to the circuit in an attempt to bring the current and voltage back in phase. This will bring the power factor closer to unity, but a value of 0.9 may be more realistic. If you can't find this information, some guesswork comes into play: Use the industry-standard average of 0.6, which represents an average power factor. For high-power motors, the power factor may be much lower, potentially even as low as 0.35.

Step 2

Convert the power factor percentage value into a decimal. This is done by simply dividing the percentage value by 100. For example, 85 percent becomes 0.85. If it is already in decimal form (a number between zero and one) then you don't need to perform a conversion.

Multiply kVA by the power factor to calculate kW.

Convert your kVA value into kW using the following formula, where "kW" is the real power you are trying to calculate and "kVA" is the apparent power. "PF" refers to the power factor of the appliance, in its decimal form. The formula is: kW = kVA x PF