What size generator do I need for my house?

Last Updated on July 25, 2022 by Jahangir

In the event of a power outage, a generator is vital to provide power for a home or a business. In times when your home’s main electrical service is unavailable or not working properly, a standby generator provides continuous, reliable backup electricity. Additionally, it protects your electric system from under voltages and other problems. However, what size generator do I need for my house? You can choose the right type of generator for your needs with the following information:

What size generator do I need to run my whole house?

In order to purchase a generator, we have to decide what kind we need. Diesel engines are more efficient, so we can choose them. A regular gasoline engine generator would suffice if you want to power a small appliance like a TV, light, or fan. The next step is to determine the power requirements of each individual piece of electrical equipment. Adding amps and volts is simply a matter of multiplying them together or checking the equipment specifications to get the wattage. In order to determine the required size of the generator, I divided the significant tasks into some steps. Here are the details-

What size generator do I need for my house

Step 1 – Make the list of devices you want to run

It is imperative that we first determine how many lights are in our home. Secondly, we need to find out the number of electric fans in our house. Next, we should figure out how many electric water heaters we have in our home. In addition, we should find out how many televisions or other electrical devices we have in our home. In this case, I considered 10 LED lights, 5 Fans, 3 AC, 1 Refrigerator, 1 water pump and 1 TV to be the significant devices that needed to be powered.

Step-2:  calculate the total power requirements for your selected appliances.

Calculate the total wattage of your required equipment once you have completed the list of equipment. Hence, the total wattage can be calculated according to the following: –

It is important to note two things: the starting current may be higher than the running current of some electrical devices like water pumps, air conditioners, refrigerators, and so on. The manufacturer of the equipment will provide you with information regarding the equipment. There is no need to worry in this regard. Because the wattage of an electrical device can differ between manufacturers, this rating is always checked.

Power in watt: Sometimes, you can find the unit of the equipment other than watt as shown in the below picture.

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What size generator do I need for my house?

In this case, you need to convert this unit to watt. If we consider the above technical specification, here the power of the pump/motor is 0.75Hp. We know 1Hp is equal to the 0.746 Kilowatts. Then 0.75Hp=0.55KW. This is also mentioned in the above specification. But, some manufacturers do not display in KW. They only show the unit in HP. However, now convert the KW to W and we know 1000Watts is equal to 1KW. So the watt of this water pump is 0.55KW=0.55*1000=550watts

Step 3- Consider safety factor

Once you find the total watt of your electrical devices, you should consider the safety factor as 20%. This will help you to protect your generator from overload and in case if you want to increase the load in future, then you can do it. So, the safety factor is very important to consider during buying your first generator. From the above calculation, we have found the total load of the house is 6400Watts. Now consider the safety factor as 20%, then the total load


Step 4 – Convert watt to VA to calculate the size of the generator

Now, we can calculate the size of the generator. The formula is simple. In most cases, the generator manufacturers use the generator capacity as VA i.e. Volt*Ampere.  This is very simple to convert the watt to VA. In this case, we will apply the most common as well as very important formula as P=V*I*Cosθ [I have considered single phase because most of our house/home is used single-phase current].

Here, V*I is the VA and Cosθ is the power factor. The average power factor is 0.80. So I am assuming the power fact is 0.8 in this case.

So, we get, 7680=VA*0.8


So, you should select a 10,000VA generator for the above load. You can easily calculate the size of your required generator by using the above calculation. If you still face any issues, please contact us. We will help you to sort out your required generator.


Unlike what many people think, the generator size is independent of the house size. You need to consider the electrical appliance that you have to use on the generator. In fact, many homeowners need to continuously power a variety of electric appliances. For example, if you have a computer, cable TV, a water heater, a washer/dryer, and several other small appliances, you will probably need a much larger generator than someone with only one or two electrical appliances.

If you want to run a 200amp load with the help of a generator, then you can easily calculate the size of the generator by using the below formula.
We know VA=V*I
Here V=220Volts and I =200Amp, Here, I have considered the single-phase system
So, you need a 44KVA generator or 44*0.8=35.2KW generator for your 200amp service/load.

Ans: This is the same as the above question. Just check the watt of your refrigerator and freezer. You can find this information that is mentioned in a small sticker on the backside of the refrigerator and freezer. If it is 600+600=1200watts then divide with the power factor, so 1200/0.8=1500VA. So, select a generator of 1200watts/1500VA generator for running this refrigerator and freezer.

An air conditioner unit that has a 3 ton capacity uses approximately 3500 watts of electricity in an average hour.An air conditioner unit that has a 3 ton capacity uses approximately 3500 watts of electricity in an average hour. Therefore, divide this wattage by power factor=3500/0.80=4375VA. Hence, we need to select 4.5KVA generator to run this 3 ton AC. 

It will totally depend on your electrical devices that you need during the camping. Just add all the wattage of the equipment after that divide it by power factor. So, you will get the generator capacity that you require during camping. 

Ans: If the voltage of the RV is 12volts, then the total power of the RY would be as P=12*30=360watts. Therefore, we need to select at least 360watts generator to run 30Amp RV.