How to Determine the Power of the Generator?

The first thing a person need to do is to determine the power you need before purchase a generator. If your generator is not capable of serving the power you need, this may cause damage to your generator, no matter which power you are using in Standby or Prime. The exact process of determining the power of the generator, requires many considerations and depending on many factors.

Some criterias may cause confusion in this process like three phase, single phase, Kw, kVA, Prime and Standby.This article is published to avoid this confusion and to clarify the key issues related to the generator power determination process. Although it does not give as detailed technical information as a certified electrician, it enlightens the user on some important key points.

Generator Power Range:  Thanks to the developments in the field of electrical engineering, the generators produced cover a wide power range. Industrial Generators power ranages are usually in between 50kW – 3 MW while Generators for common use like Office and for house use are usualy in between 5kW – 50kW.

Power Size of the Generator: Many people thinks that they can provide “Standby (continuous/uninterruptable) Power” with less size of generator since it does not have to work continuously. Unfortunately, this is one of the most common mistakes made when purchasing a generator, and it can cause damage to your new generator as well as damage to the equipment in the facility it feeds and stop the work connected to these equipment. The key point to remember here is; A generator with a higher power than the required power should be preferred.

How to Determine the Right Size Engine or Generator?: While they do not replace the exploration and calculations of a certified electrician, the following items can be a starting point for you to follow the right path:

Knowing your needs well:  Going to a dealer and purchasing the best and the cheapest generator available is not the right approach. It is always better to determine in detail the electrical power you need before making a choice. You can do this in the following ways:- Make a list of items that need to be fed by the generator.

– Note the starting and operating powers of the relevant items.

– Calculate the total power requirements in kVA or kW.

How to Determine Starting and Operating Power:  : Determining the starting and operating power of the devices to be fed by the generator is very important for the correct power requirement calculation. Normally, you can find this kind of information on the label on the device or in the user manual.

Amper – Watt Conversion: The power requirements of devices are usually specified in amps. To convert the power requirement from amps to watts, you can do the following calculations:

For resistive load: Watts = amps x volts

For reactive load: Power = (ampere x volt) x power factor

Power Consumption Chart If you cannot access the user manuals of the electrical equipment you use, you may not be able to access the power consumption values. You can find the approximate power values of commonly used devices in the power consumption table below. In this table, you can easily see that the starting and operating powers are different.

Power Consumption Chart
This table shows how power ratings vary between different types of electrical devices. The values reflected in this table are not a definitive guide for calculating your power requirements. For the most accurate calculation, consult the user manual of each device or a professional electrician.


Product Starting Power (W) Operating Power (W)
Circle Saw 2.400 1.200
Drill 1.800 720
Edger 2.400 960
Chainsaw 2.400 1.200
Lawn Mower 4320 1.440
Pressure Washer 3600 1.200
Carwing Saw 1.800 720
Buzz Saw 2.100 840
Electric Sander 1.800 600
Paint Sprayer 1.080 360
Planer 2.400 960
Router 1.500 600
Water Pump 3000 1.000
Wet / Dry Vacuum 2.500 888
Crane 5400 1.800
Oven Fan, Gas/Fuel Oil Oven
     1/8 horsepower (hp) (hp) 500 300
     1/6 horsepower (hp) 750 500
     1/4 horsepower (hp) 1.000 600
     2/5 horsepower (hp) 1.400 700
     3/5 horsepower (hp) 2.350 875
Central Air Conditioning
     10.000 BTU 2.200 1.500
     20.000 BTU 3300 2.500
     24.000 BTU 4950 3800
     32.000 BTU 6500 5000
     40.000 BTU 6700 6000
1/4′ Drill 300 300
Belt Sander 1.000 1.000
Disk Sander 1.200 1.200
Twist Saw 3100 1.560
12′ Concrete Cutter 3600 1.800
7 1/4′ Saw 3000 1.500
Grinder Disk 4000 2.000
Air Compressor (Average) 4000 2.000

Different methods of calculating power:  There are several different ways to calculate power requirements, depending on the type, number of devices, and the generator’s usage plan:

– With one engine running.
– When multiple engines are running simultaneously.
– Without electric motors

Advantages of choosing a generator of suitable power: By now you’ve got the idea to choose a suitable generator for your needs, here are a few of the benefits gained from following these processes:

– Elimination of unexpected system errors,
– Elimination of shutdowns due to overload,
– Generator has longer durable
– Performance guarantee.
– Proper and trouble-free maintenance
– Increased system duration
– Ensuring personal security

Where to Buy, the Role of Service Providers and Dealers:  Since the generator will be used for continuous or emergency electricity requirements (perhaps in a crisis), choosing the company you will buy is an important issue that should not be ignored. It is necessary to examine all of the issues such as how many years of experience the seller has, whether it provides service and spare parts, how fast a response is provided, and the capability of giving special attention to urgent matter.