What size generator do I need? (Generator Size Guide)

Buying a generator can be a daunting task with millions of different options available to you. Some questions you may ask yourself are: What fuel type should I go for? What oil shall I use? And even, How do I start the generator? Here at Generator Pro, we aim to make the process of buying a generator as simple as possible so today we are going to tackle the subject of: What size generator do I need?

First Things First…

If you are reading this article then you probably have an idea of why you need a generator, you probably have a list of appliances you want to power. But the question you need to ask yourself is: what items do you want to power simultaneously? For example, you may have a luxurious campervan which has an electric cooker, television, microwave and washing machine. However the chances are you won’t be using all these products at the same time.

Checking the Power Label

Morphy Richards Power Rating Sticker

Now you have a good idea of what you want to power, you now need to work out the wattage the appliances require. All appliances sold in the UK will have a sticker similar to the one shown above outlining an approximate power consumption of the product. Add these values together for the appliances you want to run simultaneously and use this as a guide for your needed power consumption.

What if I can’t find the sticker?

All appliances are different so if you cant find a sticker on the product itself, we would always advise googling the model number. If you are unlucky with your search and still cant find a power rating, here is a rough idea of the power consumption of different products:


Approximate Starting Wattage
Approximate Running Wattage
240V required?
Refrigerator or Freezer (Energy Star)1200132-192 
Microwave Oven
650 watts10001000 
800 watts13001300 
1000 watts15001500 
Incandescent Lightsas indicated on bulb (i.e. 60W)as indicated on bulb (i.e. 60W) 
Furnace Fan, gas or fuel oil 
 1/8 Horsepower   500300Y
 1/6 Horsepower750500Y
 1/4 Horsepower1000600Y
 1/3 Horsepower1400700Y
 1/2 Horsepower2350875Y
 Tube type300300 
 Flat Screen (20”)120120 
 Flat Screen (46″)190190 
 Coffee Maker (4 cup)600600 
 Dishwasher (Cool Dry)540216 
 Electric Fry Pan15001500 
 Electric Range (8-inch element)21002100Y
 Automatic Washer12001200 
 Clothes Dryer (Electric)67505400Y
 Radio50 to 20050 to 200 
 Sump Pump 
 1/3 Horsepower1300800Y
 1/2 Horsepower21501050Y
 Window Air Conditioner (10,000 BTU)22001500 
 Monitor (LCD style)3030 
 Hot Water Heater45004500Y
 Garage Door Opener1420720 
Approximate Starting Wattage
Approximate Running Wattage
240V required?
 Tube type300300 
 Flat Screen120120 
 RV Air Conditioner   
 11000 BTU1600 1010  
 13500 BTU28001800 
 15000 BTU 3300 2000 
 RV Refrigerator 600180 
 Electric Grill (tabletop) 1650 1650 
 Slow Cooker170-270170-270 
 Hair Dryer (1600 watts)19001800 
 Microwave Oven (650 watts)10001000 
 Coffee Maker600600 
 Radiant Heater13001300 
 Laptop computer200-250200-250 
 Satelite Receiver 250 250 
 Radio50 to 20050 to 200 
 Two-Way Radio   
 Fan (portable)120 40 
 DVD Player350 350 

Power Tools:

Approximate Starting WattageApproximate Running Wattage
 Air Compressor
 1/2 hp1600975
 1 hp45001600
 Bench Grinder (8 in.)25001400
 Circular Saw (Heavy Duty, 7 1/4 in.)23001400
 Concrete Vibrator
 1/2 hp840 (avg.)840 (avg.)
 1 hp1080 (avg.)1080 (avg.)
 2 hp1560 (avg.)1560 (avg.)
 3 hp2400 (avg.)2400 (avg.)
 Demolition hammer1260 (avg.)1260 (avg.)
 Drain cleaner250 (avg.)250 (avg.)
 3/8 inch, 4 amps600440
 1/2 inch, 5.4 amps900600
 Electric Chain Saw (14 inches, 2 hp)11001100
 Hand Drill (1/2 in.)900600
 High-pressure Washer (1 hp)36001200
 Rotary hammer1200 (avg.)1200 (avg.)
 Table Saw (10 in.)45001800
 Industrial Motors  
 Split Phase
 1/8 Horsepower1200275
 1/4 Horsepower1700400
 1/3 Horsepower1950450
 1/2 Horsepower2600600
 Capacitor Start Induction Run
 1/8 Horsepower850275
 1/4 Horsepower1050400
 1/3 Horsepower1350450
 1/2 Horsepower1800600
 3/4 Horsepower2600850
 1 Horsepower30001000
 1 1/2 Horsepower42001600
 2 Horsepower51002000
 3 Horsepower68003000
 4 Horsepower98004800
 Capacitor Start Capacitor Run
 1/8 Horsepower600275
 1/4 Horsepower850400
 1/3 Horsepower975450
 3/4 Horsepower1900850
 1 Horsepower23001000
 1 1/2 Horsepower32001600
 2 Horsepower39002000
 3 Horsepower52003000
 4 Horsepower75004800
 Fan Duty
 1/4 Horsepower1200650


Approximate Starting Wattage
Approximate Running Wattage
  Electric Fence, 25 miles250250
  Milk Cooler18001100
  Milker (vacuum pump, 2hp)23001000
  Portable Heater (kerosene, diesel fuel)
  50,000 BTU600400
  90,000 BTU725500
  150,000 BTU1000625
  Battery Charger
  15 amp380380
  60 amp with 250-amp boost1500/57501500/5750

The Final Steps

So now you know what size generator you need and are ready to find the perfect generator for you. We would always recommend getting a slightly larger generator then what you need to make sure you are protected incase you decide to run something else on it. For example: if your calculations estimate that you will need 2200W then maybe look at a 3000W generator. This will also help with fuel consumption and limit stress on the generator saving you money in the long run. You can search for the perfect generator on our website, filtering by Generator Output. If you have any questions then feel free to contact us directly or check out our frequently asked questions album on our Facebook page.

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