Generator power output is usually expressed in VoltAmps (VA) and, occasionally, in Watts (W).
When the numbers get into the thousands, these terms become kiloVoltAmps (kVA) or kilowatts (kW).
For our purposes the rule of thumb is that 1000VA is about 800W.
To convert from Watts to VA, multiply Watts by 1,25 (and vice versa).
Also, you want your generator to be rated at least 30% higher than what you need.
Want to run twenty 100W light bulbs?
20 x 100W = 2000W (2kW).
2kW plus an extra 30% reserve = 2,6kW.
Need that in VA because that’s how the generators are marked ?
2,6kW x 1,25 = 3.25kVA.
So, your twenty 100W light bulbs need a 3,25kVA (or bigger) generator.
What size then?
Simply add up the rated power of every electrical device you need to have running off the generator simultaneously.
Here are some examples of common items:
- Normal domestic light bulbs: 60W to 100W
- Energy-saver light bulbs: 10W to 20W
- TV: 150W
- PC: 250W
- Laptop: 100W
- Desk fan: 30W
- Food blender: 50W
- Kitchen fridge/freezer: 200W
- Bar fridge: 100W
- Kettle: 1200W
- Stove plate: 1500W
- Oven: 2000W
- Tumble dryer: 3000W
- Geyser: 3000W
- Vacuum cleaner: 1000W
- Lawnmower: 3000W
- Pool pump: 1200W
One notable exception: Air conditioners.
Although your air conditioner may be rated at, say, 3kW, it draws a startup surge every few minutes that is a few times this figure. Your generator will choke on this unless it’s well up to the job of providing this brief surge current. For most folks this means forgetting about using the aircon and surviving with a desk fan instead. If you must use your aircon then you’ll need a generator rated at least twice the power of your aircon’s rating, possibly more.