Generator Watts, Volts, and Amps

Electrical terms get tossed around like baseballs at spring batting practice, and while we are familiar with hearing them, do we really know what they mean?

polemanWhen considering the purchase of a generator, whether for a home standby unit, portable job-site electrical power, or to install in a boat or RV, correctly applying and using terms like volts, watts, and amps can make the difference between correctly-sizing a generator that does that job, or choosing one that is under or over powered. After the purchase is made, it is still important to understand the terms and apply them to keep from overloading the generator or tripping circuit breakers.


Electricity is the flow of electrons through a conductor. Amperes, or amps, is a measure of how many electrons are flowing. The flow of electrons through a conductor is called electric current. It takes many electrons to do even a small amount of work; one ampere is equal to 6.241 x 1018 electrons flowing in one second.

When electrons flow, they meet resistance in whatever conductor they are flowing through. The larger the conductor, the less resistance they meet. When electrons flow against resistance, they create heat. A wire conductor can grow hot enough to ignite flammable materials if it is too small to carry the current. For this reason, wires in homes are required by code to be a certain size and protected by circuit breakers or fuses that open if the safe current level is exceeded.

Generators are capable of producing a limited number of amperes and are protected by circuit breakers that prevent overloading the generator.


Voltage is pressure, very much like water pressure in a hose or pipe. It is the force that moves electrons through a conductor. The higher the pressure, the more work the electrons are capable of doing.

Image 843Water under pressure can do work such as cleaning a sidewalk or stripping paint from a house, as long as there is enough water and pressure to do the job. The same is true of electricity. If you have electrons moving with pressure behind them, they will do work such as turning a motor, heating a light bulb filament until it glows, or producing heat in a space heater.

Appliances are often rated by the number of volts they require, and the number of amps they use to do the work for which they were designed.

Watts and Kilowatts

Power is the amount of work done in a specific amount of time. The unit used to express power is watts and is a function of both current and voltage. To find the power electricity is doing, multiply amperes by voltage to obtain watt-hours. Another common unit is kilowatt-hours, which is simply watts divided by 1000. One kilowatt = 1000 watts.

Generators are rated in watts or kilowatts to express how much work they are capable of doing. Just as an athlete might put out a burst of extra energy in a sprint for a few seconds, a generator can do the same thing and put out a surge of extra power for a few seconds. This extra capacity allows it to start electric motors which require an initial boost of power to start turning.

These examples illustrate the relationship between volts, amps, and watts.

  • 12 volts x 200 amperes = 2400 watts.
  • 120 volts x 20 amperes = 2400 watts.
  • 240 volts x 10 amperes = 2400 watts.
  • 12 volts x 10 amperes = 120 watts.
  • 120 volts x 10 amperes = 1200 watts.

In the first three examples, note how more amperes are required to produce the same power at a lower voltage than a higher voltage. In the last two examples, increasing the voltage while keeping the amperes the same increases the power.

Generator Power

Electricity has changed the world with its ability to do work. As our reliance on the supply of electricity grows, so does its impact on our lives when it is suddenly not available. It keeps our homes safe, dry and warm, powers appliances and tools that make our lives easier, and extends the shelf life of the foods we eat.

Understanding the simple electrical terms that describe the work a generator does helps make choices when selecting a new generator and operating it safely and efficiently after the purchase.

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