Power Consumption or Demand is quantified in Watts

1000 Watts = 1 kW (kilowatt).

All appliances, lighting, equipment, machines have a maximum power consumption rating or continuous usage requirement in Watts.

However all Generator Sets are classified in kVA.

Therefore to determine what size generator we need we have to convert from kVA to kW

Therefore:  kVA × 0.8 = KW.  Where 0.8 is the Power Factor.

To determine the size of Generator we need we have to convert from the required kW power consumption to the kVA required to be generated. 
Therefore: kW ÷ 0.8 = kVA. Where 0.8 is the Power Factor.
Example:
A Kettle using 2000 Watts to heat up water requires:
2000W ÷ 0.8 = 2500VA or 2.5 kVA Generator minimum.

Remember a Generator has a Maximum Output kVA for very short periods and a continuous output (rating) called Rated Output in kVA. Use this Rated Output specification in your calculations when determining the size of the Generator you need.

VERY IMPORTANT
REACTIVE POWER LOADS:

Electrical equipment such as those that have motors need more power when being started and therefore demand up to 3 times greater generating power than during their normal continuous consumption. The power consumptions listed above already include this greater power requirement for start-up.
Example:If a Freezer (with an electric motor in its Compressor) uses 500 Watts normally, then on start-up it would draw up to 1500 Watts from the Generator.

At 1500 Watts the generating power required is 1500W ÷ 0.8 = 1875VA or 1.9kVA.