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Wattage Calculator

There are different categories to consider when choosing a generator for your needs: recreation, home standby and construction. You may also want to consider using an inverter generator for sensitive electronic devices. Inverter generators are smaller and lighter as power is created electronically and not through a conventional alternator. Inverter power offers the cleanest power output.

If you want a generator for home standby, say to run your refrigerator, youíll need at least 2500 watts or more. And if you want to use a transfer switch so that power can go directly into your home, youíll want a generator with at least 3000 watts.

Youíll also need to consider the maximum and rated power of the generator. This is important depending on what items you want to run off of your generator. Items such as toaster, lamps, and coffee makers are resistive, or constant loads and their total load can be calculated at amps x 1. Items such as saws and drills are reactive loads and while the running load may be small, the starting load should be calculated at running amps x 3. Remember, after the intial start less power is required for actual operation.

Always remember that simple power management will allow a smaller generator to do a big job. Very seldom are all tools or appliances operating simultaneously. When calculating power requirements, consider the starting requirements are only for the initial start and then additional tools may be operated in addition.

Remember Ohmís Law
Watts = Volts x Amps
Amps = Watts/Volts

So, if you have two of the numbers (e.g. volts, amps) then you can find out the other (e.g. watts). This can help you to determine the rated power that youíll need from your generator.

AVERAGE WATTAGE REQUIREMENT GUIDE
(AMPS X VOLTS = WATTS)

Household
Running
Wattage
Requirements
Additional
Wattage Required
For Starting
Coffee Maker 1750
0
Dishwasher
Cool Dry
700
1400
Electric Fry Pan 1300
0
Electric Range
8-inch element
2100
0
Microwave Oven 625 watts
625
800
Refrigerator or Freezer
700
2200
Automatic Washer
1150
2300
Clothes Dryer
Electric
5750
1800

Furnace Fan, gas or fuel oil
1/8 Horsepower 300
500
1/6 Horsepower 500
750
1/4 Horsepower 600
1000
1/3 Horsepower 700
1400
1/2 Horsepower 875
2350
Lights as indicated on bulb (30 to 100)
0
Radio
50 to 200 0

Sump Pump
1/3 Horsepower 800
1300
1/2 Horsepower 1050
2150
Television - Color 300
0
Central Air Conditioner
10,000 BTU
1500
2200
Contractor
Running
Wattage
Requirements
Additional
Wattage Required
For Starting
Air Compressor
1 Horsepower
1500
4500
Bench Grinder
8 inches
1400
2500
Hand Drill
1/2 inch
600
0
High-pressure Washer
1 Horsepower
1200
3600
Circular Saw, Heavy Duty
71/4 inches
1400
2300
Electric Chain Saw
14 inches, 2 Horsepower
1100
0
Table Saw
10 inches
1800
4500

Drills
3/8 inch 4 amps 440
600
1/2 inch 5.4 amps 600
900
Industrial Motors
Running
Wattage
Requirements
Additional
Wattage Required
For Starting

Split Phase
1/4 Horsepower 600
1000
1/2 Horsepower 875
2300

Capacitor Start Induction Run
1/3 Horsepower 720
1300
1 Horsepower 1600
4500

Capacitor Start Capacitor Run
11/2 Horsepower 2000
6100

Fan Duty
1/4 Horsepower 650
1200
Farm Equipment
Running
Wattage
Requirements
Additional
Wattage Required
For Starting
Electric Fence, 25 miles 250
0
Milk Cooler 1100
1800
Milker (vacuum pump),
2 Horsepower
1000
2300

Portable Heater (kerosene, diesel fuel)
50,000 BTU 400
600
90,000 BTU 500
725
150,000 BTU 625
1000

Battery Charger
15 amp 380 0
60 amp with 250-amp boost
1500/5750 0
100 amp with 300-amp boost
2400/7800
0

Electric Welder
200 amp AC 9000 0
230 amp AC, at 100 amp 7800 0
Air Compressors Running
Wattage
Requirements
Additional
Wattage Required
For Starting
1/2 Horsepower 975 1600
1 Horsepower 1600 4500

Computers
Running
Wattage
Requirements
Additional
Wattage Required
For Starting
Desktop 600 to 800 0
Laptop 200 to 250 0
Monitor 200 to 250 0
Fax 600 to 800 0
Printer 400 to 600 0
Needed to Start
Minimum:
Minimum:
Needed to Run
Minimum:
Minimum: