How do I convert amps to watts?
Appliances frequently list their power requirements in amps. Most generators list their output in watts. Fortunately, it’s easy to convert from one to the other:
 Watts = Volts x Amps (Volts times Amps)
 Amps = Watts/Volts (Watts divided by Volts)
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 you’ll need from your generator.
Starting vs. Running Wattage
Some appliances require extra power to start up, while others maintain the same power requirements constantly.
To calculate your power needs correctly, you need to know which kind of load you are dealing with. (A load is defined as the device that you are powering.) There are two kinds of loads:
Resistive loads
Resistive loads are pretty simple: they require the same amount of power to both start and run the equipment. Many resistive loads are involved in heating or making heat of some kind. Examples of resistive loads include:
 Light bulbs
 Coffee maker
 Toaster
Reactive Loads
Reactive loads contain an electric motor, which requires additional power to start, but significantly less power to run once it gets going. Typically starting power is 3 times the amount of power to run the application. Examples of reactive loads include:
 Refrigerators / freezers
 Furnace fans
 Well pumps
 Air conditioners
 Bench grinders
 Air compressors
 Power tools
Some household appliances, like a furnace or refrigerator, have internal fans that come on intermittently. Extra wattage/power is needed to start the fan each time. Refrigerators also have a defrost cycle that requires power in addition to the compressor and fans.
Reactive loads may also require additional power when the electric motor begins to work. For example, when a saw begins cutting wood, its power requirement will increase. This is not applicable for most household appliances.
My appliance is a 1000 watt model, but it takes 1600 watts to run it. Why?
Some devices are labeled or promoted with a power number. For example, a hair dryer might say "1000W." This means the hair dryer itself produces 1000 watts of heat energy. But the amount the hair dryer uses from a power outlet is always more than it produces in heat. This is because the device’s energy use is not 100% efficient.
Another example is a microwave oven. It may be marketed as "1100 watt oven" and indeed produce 1100 watts of cooking power, but it will require more than that from a generator.
Translating the data tag:
For some appliances, you can determine the power needed by looking at the data tag supplied by the electric motor manufacturer.
All electrical motors should have a data tag attached to their bodies that give volts, amps, phase, cycles, hp, and sometimes a code.
 Volts (V)  The volts must be either 120 (110120) or 120/240. 120/240 means that the motor can be wired to operate on 120V or 240V. Honda generators are either 120V or 120/240V.
 Amps (A)  Indicates the amps required to RUN the electric motor but doesn't consider STARTING or LOADED power requirements.
 Phase (PH)  Honda Generators can only power single phase motors.
 Horsepower (HP)  Rating of how much work an electric motor can perform.
 Code  This isn't always provided on the data tag. It represents the maximum STARTING power required of the electric motor. You can multiply the code (amps) times the Horsepower of motor to determine starting amps. Find a list of codes and the amps here.
 Cycles (Hz)  All U.S. electrical appliances run at 60 cycles per second.
To determine the wattage needed, use
Amps x Volts = Watts (Amps times Volts = Watts)
Maximum vs. Rated Power
Generators are often advertised at the maximum wattage they can produce. But you’ll also see the “rated power” listed.
 Maximum power = the maximum output that a generator can produce. Maximum power is usually available for up to 30 minutes.
 Rated power  the power that a generator can produce for long periods of time. Typically 90% of the maximum power.
In general, use rated power to determine if a generator will be able to adequately power your applications continuously.
Wattage Estimation Guide
Contractor Applications

Approximate Running Wattage 

Air Compressor ½ hp  1600  1975 

Air Compressor 1 hp  4500  1600  
Bosch Grinder (8 in.)  2500  1400  
Concrete Vibrator ½ hp  840 (avg)  840 (avg)  
Concrete Vibrator 1 hp  1080 (avg)  1080 (avg)  
Concrete Vibrator 2 hp  1560 (avg)  1560 (avg)  
Concrete Vibrator 3 hp  2400 (avg)  2400 (avg)  
Demolition Hammer  1260 (avg.)  1260 (avg.)  
Drain Cleaner  250 (avg.)  250 (avg.)  
Drills 3/8 inch, 4 amps  600  440  
Drills 1/2 inch, 5.4 amps  900  600  
Electric Chain Saw (14 inches, 2 hp)  1100  1100  
Hand Drill (1/2 in.)  900  600  
Highpressure Washer (1 hp)  3600  1200  
Rotary hammer  1200 (avg.)  1200 (avg.)  
Table Saw (10 in.)  4500  1800  
Fan Duty ¼ horsepower  1200  650 
Approximate Starting Wattage  Approximate Running Wattage  

Split Phase 1/8 Horsepower  1200  275 
Split Phase 1/4 Horsepower  1700  400 
Split Phase 1/3 Horsepower  1950  450 
Split Phase 1/2 Horsepower  2600  600 
Capacitor Start Induction Run 1/8 Horsepower  850  275 
Capacitor Start Induction Run 1/4 Horsepower  1050  400 
Capacitor Start Induction Run 1/3 Horsepower  1350  450 
Capacitor Start Induction Run 1/2 Horsepower  1800  600 
Capacitor Start Induction Run 3/4 Horsepower  2600  850 
Capacitor Start Induction Run 1 Horsepower  3000  1000 
Capacitor Start Induction Run 1 1/2Horsepower  4200  1600 
Capacitor Start Induction Run 2 Horsepower  5100  2000 
Capacitor Start Induction Run 3 Horsepower  6800  3000 
Capacitor Start Induction Run 4 Horsepower  9800  4800 
Capacitor Start Capacitor Run 1/8 Horsepower  600  275 
Capacitor Start Capacitor Run 1/4 Horsepower  850  400 
Capacitor Start Capacitor Run 1/3 Horsepower  975  450 
Capacitor Start Capacitor Run 1/2 Horsepower  1300  600 
Capacitor Start Capacitor Run 3/4 Horsepower  1900  850 
Capacitor Start Capacitor Run 1 Horsepower  2300  1000 
Capacitor Start Capacitor Run 1 1/2Horsepower  3200  1600 
Capacitor Start Capacitor Run 2 Horsepower  3900  2000 
Capacitor Start Capacitor Run 3 Horsepower  5200  3000 
Capacitor Start Capacitor Run 4 Horsepower  7500  4800 