An Overview of Generator Sizing Calculation

Generator Sizing Calculation Overview

Purchasing a generator requires significant capital and in many cases, is a one-time investment.

A good purchasing decision must, therefore, involve the choice of a generator that will handle all your power requirements.

Many factors affect the size of a generator you need making it very difficult to make a straightforward decision on generator size.

Generator Sizing Calculation

An oversized generator may cause stress and damage to devices connected to it, while an undersized generator may not power up all your devices as required.

A generator calculator helps you determine the size of a generator you need by factoring in all your power consumption needs.

How to calculate what size generator I need?

The size of a generator mainly depends on the total power use of all your equipment in wattage.

You should start by making a list of all equipment consuming power in your particular setting.

Alongside each piece of equipment on the list should be an indication of the power requirement of each piece of equipment in watts.

Finally, the total of your power requirement should be calculated as this is what determines the size of the generator you need.

You should choose a generator that is slightly larger in capacity to cater for under-performance cases of the generator or replacement of equipment with a higher power requirement.

Home generator sizing calculator

Although home power requirements are relatively lower, proper calculation of generator size is still needed.

Most of the home generator calculators available online require you to feed information on the power usage of the home equipment that you would want to keep running after a power outage.

On feeding all your wattage figures, the total is calculated and the size is determined for you automatically.

Commercial Generator Sizing Calculator

Since power outages in business areas such as industries may cause substantial financial liabilities if not addressed on time, an excellent-sized generator must be available.

The facility’s square footage and peak usage in real-time are what is needed in a commercial generator calculator.

An Overview of Generator Sizing Calculation

On the calculation of the total kilowatt required, a generator size is selected for your commercial power backup.

To ensure that you are not overwhelmed with all these considerations when choosing a generator size, it is essential to use a generator calculator.

Tons of software are available online to assist in generator sizing.

Generator Calculation

Purchasing a generator is a huge investment for a home or a business owner. It is also something not a lot of people buy, meaning there is a lot of confusion on calculating the generator load and sizing.

The best call is to consult an electrician, but if you decide to do a generator calculation by yourself, you can, by following a few basic rules.

Generator calculation (size)

The primary method in sizing a generator is as follows. Firstly you must create a list of all the items that will be powered by the generator.

Afterward, you must determine the starting and running wattage for each piece of equipment.

Those are the energies needed to turn the equipment on and to operate it. Usually, these are written on the equipment itself.

Finally, you can calculate the total power needed by adding up those figures and purchasing a generator that has a 10-20% larger capacity.

Generator calculation (load)

When calculating the generator load, you must first consider that there are two ways of generators being rated.

With kilo-volt-ampere (kvA) and with kilowatts (kW).

There is also a difference in the formulas depending on whether you have a single or a three-phase generator.

The formulas are:


Single-phase: Amps X Volts = Watts / 1000 = Kilowatts

Three-phase: Amps X Volts X 1.73 (Power Factor) = Watts / 1000 = Kilowatts


Single-phase: Volts X Amps / 1000 = kvA

Three-phase: Volts X Amps X 1.73 (Power Factor) / 1000 = kvA

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