You need to consider evaluating the right size of a generator before you make the decision to buy it for your home, office or factory. One of the most important questions to ask when looking for a powerful generator to purchase is, “how many volts should a generator put out?”

This guide explains all you need to know about this issue. Fortunately, the calculation is straightforward and so will help you in saving a lot of time, money, and energy.

### Calculating Watts and Kilowatts a Generator Supplies

Power is a term representing the amount of work that’s done in a specific amount of time. Watts is the unit used for expressing power and is a function of both voltage and current.

As a standard rule, companies rate the power output of a generator in watts (W) or kilowatts (kW, an equivalent of 1000W).

The formula is Watts = Volts X Amps.

Thus, when you buy a 5kW generator that produces 120 Volts (V), it can deliver an output of 41.67 amps (A). In the same vein, dual-voltage generators can provide an output of 120V and 240V.

When you multiply amperes by voltage in a specific time, you obtain a value for power in watt-hours (WH) or kilowatt-hours (kWH), which is another common unit with 1 kWH being an equivalent of 1000 WH.

Generators are rated in Watts or Kilowatts to show how much work they’re capable of doing. The following examples express the relationship between amps, volts, and watts and why we make use of watts or kilowatts for rating a generator, and not volts or amps.

Voltage (Volts) |
Current (Amps) |
Power (Watts) |

12 V | 200 A | 12 x 200 = 2400 W |

120 V | 20 A | 120 x 20 =2400 W |

240 V | 10 A | 240 x 10 = 2400 W |

12 V | 10 A | 12 x 10 = 120 W |

120 V | 10 A | 120 x 10 = 1200 W |

In the first 3 examples in the table above, we can see that more current (measured in amps) is needed to generate the same power (measured in Watts) at a low voltage (measured in Volts) than is required at high voltage. However, in the last 2 examples, when the voltage is increased and the current is kept constant, the same increases the power.

In North America, the standard house current is 120V, but certain appliances make use of 240V. Home standby generators and the majority of portable generators have the capability to supply either 120V or 240V and do this at the same time. With different voltages, it becomes important to understand the reason for rating generators in watts. In terms of capacity, it’s the power in watts that’s really important.

For instance, compare a window air conditioner (AC) operating on 120V at 12A (120V x 12A = 1440 Watts) with the small burner on an electric stove that has 1200 Watts, but running on 240V at 5A. Our primary concern is that the generator delivers enough power. And to run these two items, a total of 2640 Watts is required (in addition to starting watts for the AC), even though they’re different voltages, drawing different amounts of current.

The term, “running Watts” (or “rated Watts”), describes the capacity of the generator for continuous power supply without tripping or overloading circuit breakers. On the other hand, Surge Watts has to do with an extra boost of power for only some seconds, which enables motors to start.

Motors on tools, ACs, and small pumps need 2–3 times their rated watts to start. To start our AC unit in the above example, a generator has to supply 4320 surge Watts at least for up to 3 seconds to start the motor.

Running Watts is an essential number to check. Sometimes, generator makers assign a model number or advertise based on the surge watts. Consider checking the specs for running watts to determine how much power the generator is able to supply continuously. If you plan on operating anything with an electric motor, surge Watts are important.

**How to Decide the Type of Generator to Purchase**

Start by preparing a list of all the electrical appliances you’re planning to power in your home, office or factory. Then, add up the power consumption in Watts to determine the generator capacity required for the power consumption.

Pay attention to the fact that specific appliances, such as ACs or electric motors, need significantly higher wattage to start, but can operate with lesser power later on. Always opt for a higher capacity generator.

For example, if all the electrical appliances in your home add up to say 5000W (5kW) or add up to 200,000W (or 200kW) in your factory, you need to get a minimum of 7.5 kW generator for the house and a 300 kW unit for the factory.

Generally, please note these:

**1–10 kW generators**: These can power homes and small offices. A 5kW generator can power up to 4 lights, a fan, a refrigerator, and an electric motor, and such basic generators are ideal for small homes. But the perfect generator for your home needs to have at least 10 kW capacity.**10–50 kW generators**: Today, people make use of many electrical appliances in their homes, including air conditioners, water purifiers, geysers, water pumps, and others. These appliances demand more power to run. For instance, appliances such as your washing machines could consume 750W but require around 2500W to start. For this reason, we recommend choosing a generator that’s a capacity higher than your standard requirement.**50–100 kW generators**: For home units, anything more than 50 kilowatts isn’t necessary. Generators within the capacity range, 50–100 kW, are ideal for offices and restaurants and can power up air conditioners, particularly central AC systems.**100–200 kW generators**: Industries & large offices require generators that have capacities more than 100 kW. Such generators are large machines that can operate for around 8–10 hours on a full tank. Industrial machines often consume a lot of power.**200–300 kW generators**: Large industries and high-rise buildings need generators that have high capacities as these units can power large machines, such as elevators and a large number of air conditioners, and others. 300 kW generators use diesel or gas.**More than 300 kW generators**: If you require workhorse generators for powering large industries and official establishments, you need to go for generators with capacities over 300 kilowatts. Such generators can power heavy machines as well as large equipment.

We hope we’ve been able to do an excellent of job of addressing any concerns you may have about the question, “how many volts should a generator put out?”