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Generator Power Calculator

Created by Anupriya Aggarwal
Reviewed by Dominik Czernia, PhD and Jack Bowater
Last updated: May 23, 2024

Are you looking for a generator power calculator to analyze the electrical energy consumption of your devices? Are you buying a generator as a power supply for your home, work, camping, or anywhere you need electricity?

Before you leave on a voyage of searching, shortlisting, and shopping, you need to have at least a ballpark idea of your power requirements – this generator power calculator will come in very handy in doing so.

In the following article, we also explain what a power generator is and how a power generator work. Keep reading!

How does a power generator work?

Let's begin by explaining what a power generator is. An electrical power generator (commonly known as a generator) is a device that converts the chemical energy of a fuel such as gasoline or diesel into electrical power. The detailed conversion would be chemical energy to thermal energy, thermal energy to mechanical, and mechanical work to electrical power. Detailing those concepts is out of the scope of this calculator, but you can find out more at the thermal energy calculator and electrical power calculator.

How does a generator power a house?
Generators are required to support electrical power requirements in many scenarios, including:

  • Home or office use in the event of a power cut;
  • Power required for temporary equipment not connected to a local power grid;
  • Difficult terrains where electric power supply is not available, e.g., camping and leisure activities; and
  • Events and shows, portable living spaces.

Generators are especially crucial for places where the potential lack of electricity may become dangerous for human life, e.g., hospitals.

The generator power calculator

The generator power calculator takes the total current requirement of the devices in amperes (A) and the supply voltage rating in volts (V\mathrm{V}) to calculate the apparent power (kVA\mathrm{kVA}), which is then used to calculate actual power based on the power factor. Check the below section if you don't understand some of the terms we used here.

You can also calculate the motor horsepower available using the efficiency of the motor and the calculated power.

What is the power factor?

The terms used in a generator power calculator might look scary at first. You don't have to worry, though. Just read on this simple explanation for each term:

  • Current (II) – The measure of the flow rate of electrons/charge flowing through a conductor's cross-section. Here we will get our value of the current by summing up the individual current rating of all devices connected to the electrical network.

  • Voltage (VV): – The difference in charge of the power source between two terminals. It is the driving force that makes the current flow through the circuit. Here we get our voltage values from the voltage rating on the devices. Note: The voltage rating of all devices should be the same; otherwise, an adequate converter needs to be used.

  • Apparent Power (SS) – A simple product of current and voltage in the circuit without considering the phase of supply. It is measured in volt-amperes and is not calculated for direct current (DC) circuits.

  • Power factor (PFPF) – The ratio of working power measured in kilowatts and apparent power measured in kilovolt-amperes. It is usually taken as 0.80.8, which means a generator is expected to work at up to 80%80\% of its maximum load capacity. Power factor is mentioned on the specifications plate of the generator. You can also calculate it, for example with Omni's power factor calculator.

  • Power (PP) – The rate at which electrical energy flows through a circuit. It is measured in watts (W\mathrm{W}). We calculate it using apparent power and the power factor. This power is used to know power requirements when buying a generator. The generator output power rating should be higher than the calculated power.

  • Efficiency (η\eta) – The efficiency of the motor is the ratio of output power to input power. Here we use it to calculate the output horsepower of the motor using the power rating measured in kilowatts. Efficiency is a widespread concept in engineering, as you can see in the efficiency calculator.

Formulas used for the generator power calculator

Now that you know what a power generator is and how a generator power a house, here are the formulas that we have used in this calculator:

Power supply type



Direct current

Apparent power (kVA)

VI/1000V\cdot I/1000

1.732VI/10001.732\cdot V\cdot I /1000

Power (kW)

VIPF/1000V\cdot I\cdot P_\mathrm{F}/1000

1.732VIPF/10001.732\cdot V\cdot I\cdot P_\mathrm{F} /1000

VI/1000V\cdot I /1000

Motor output horsepower (HP)

VIPFη/746V\cdot I\cdot P_\mathrm{F}\cdot \eta/746

1.732VIPFη/7461.732\cdot V\cdot I\cdot P_\mathrm{F}\cdot \eta /746

VIη/746V\cdot I \cdot \eta/746

Basics behind the formulas:

Single-phase alternating current means the current changes its direction of flow of charge periodically, as shown in the picture, and has a single live current wire and a neutral wire to complete the circuit. So two wires are enough for an appliance to work. It is usually used for domestic power supply.

AC single phase wave

3-phase alternating current means the current changes its direction of flow of charge periodically, as shown in the picture, and uses three live current wires and one neutral wire. The three phases are equally separated in terms of their phase cycles. The use of 1.7321.732 (the square root of 33) is present in the formula signifies the root mean squared value being taken for the three phases. This current is used in high-power motors.

AC three phase wave

Direct current means the voltage is steady at a particular level and the current always flows in a particular direction, as shown in the figure. DC also uses two wires to complete the circuit. Since there is no phase-related issues for DC, the concept of apparent power and power factor does not apply here. DC are used by all battery-operated appliances.

direct current wave


How to power a house with generator?

There are two ways to power appliances using a generator:

  1. Have dedicated appliances like emergency equipment, lighting, or ventilation. A low power generator is enough to run only the absolute essentials during a power cut.
  2. Have a complete backup attached to the main wiring of the house. A high-output generator is capable of running all appliances in the house, including high-wattage appliances.

How much generator power do I need?

Check the power rating of each appliance given in watts and calculate the total power requirement of your house before buying a generator. If the current rating is given instead of power, you can use Omni's generator power calculator to estimate the power using current and supply voltage.

Do I need to buy a generator with maximum power output?

No, you do not need to buy a generator with maximum output power. The trick to optimizing your budget without compromising on utility is the following:

Note down the combination of various appliances that usually run together. For example, some would be required for 1-2 hours a day, some in the evening/morning only. Using these groups, you can estimate the actual maximum power that would be required at any time.

What kind of appliances have power rating in watts?

Power rating is mentioned for devices with a fairly regular load, e.g., electric kettle, that will have fixed operating power. Current rating is usually mentioned on the devices with variable load, e.g., a motor with variable speed. The current will be mentioned as per full load capacity.

Anupriya Aggarwal
Generator power rating
Power supply type
AC single phase
Apparent power
Power factor
Efficiency (η)
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