Volts x amps = VA (volt-amps) x Load Factor = Watts used.

What all of this means is that it can sometimes take more current than might be apparent to operate a given device because of inefficiencies caused by its load factor. Electric motors, for example, present notoriously inductive loads and will quite often require much more current to operate (particularly starting up) than would be implied by their wattage ratings. Any time a very precise determination of power usage must be calculated, such as in configuring electrical distribution or UPS systems, it is important to take the effects of each device's load factor into account.