Generator Size Calculator Online

A Generator Size Calculator allows you to find the size of a generator that can power your home, office, shop or industrial equipment. The size of a generator you need depends on how much electricity your appliances consume.

Generator size is usually given in watts (W), kilowatts (kW) or kilovolt-amperes (kVA). The size of a generator determines how many appliances you can run on it simultaneously.

You can use this generator size calculator to find what size generator you need for your appliances and make a more educated purchase.

How To Use The Generator Size Calculator

Here are the steps to use our generator size calculator:

1. Specify which appliances and equipment you would like to use with a generator

2. Enter how much electricity each appliance consumes

3. Enter how much electricity your motor-driven appliances consume when starting

4. Enter how much additional electricity you may need if the number of appliances changes

5. Get a recommended generator size based on the information you provided

Make sure to check the appliance labels and user manuals for the electricity consumption specifications. If you have multiple appliances, you may want to specify if some of them will be used simultaneously.

Generator Size Calculator Formula

Our generator size calculator uses the following algorithm:

Step 1: Find total running watts

Generator Running Watts = Sum of the running watts of all appliances that you plan on using

Step 2: Add additional starting watts

Generator Running Watts + Additional Starting Watts = Required Generator Watts

If you have several motor-driven appliances with additional starting watts, make sure to add the largest amount of additional watts that can be expected if the other appliances are running.

Step 3: Add a safety margin

Recommended Generator Watts = Required Generator Watts × (1 + Safety Margin ÷ 100)

You can think of the safety margin as a percentage added to the required generator watts.

For example, 20% safety margin means that you need to multiply the required generator size by 1.2.

You can convert watts to kilowatts using the following formula:

Generator Kilowatts (kW) = Generator Watts ÷ 1,000

For kilovolt-amperes, you can use the following formula:

Generator Kilovolt-amperes (kVA) = Generator Kilowatts (kW) ÷ Power Factor

Power Factor depends on the type of generator and load, but 0.8 is a reasonable number for certain applications.

Generator Size Calculator Example

Let’s say you need to power the following appliances during a black-out:

Appliance Running Watts Starting Watts

Refrigerator 700 W 1,400 W

Five LED lights 50 W 50 W

Two fans 150 W 150 W

Television 120 W 120 W

Water pump 750 W 1,500 W

Total: 1,770 W 3,220 W

Assuming the numbers indicate the total starting watts for each appliance, the amount of additional starting watts would be:

3,220 − 1,770 = 1,450 W

The total amount of generator watts would be:

1,770 + 1,450 = 3,220 W

Adding a 20% safety margin would give us:

3,220 × 1.20 = 3,864 W

This means that you probably need a generator with a capacity of about 3.9 kW or more, as long as the generator can handle the in-rush of current and the appliances can start at the same time. A commercial generator with a suitable continuous rating and surge capacity would then be chosen based on the specific requirements of the application.

Interpretation of the Results

The resulting generator size recommendation is an estimate based on the information you provided.

Running watts refer to the amount of continuous power needed to run your appliances normally.

Starting watts refer to the amount of additional power needed to start motor-driven appliances.

Recommended capacity is the amount of generator power you need to account for the safety margin.

kW and kVA ratings are not interchangeable. Always make sure to use the correct units when comparing generators and appliances.

Make sure that the continuous or rated capacity of a generator is sufficient for the running watts of your appliances and that the surge capacity is sufficient for the starting watts.

Other Factors that Affect the Results

Some of the most common factors that affect the results are:

• Appliance wattage – Larger appliances consume more electricity
• Starting surges – Motor-driven appliances often require additional power when starting
• Simultaneous operation – The more appliances you use at once, the more power you will need
• Power factor – Some appliances need more power than specified
• Ambient conditions – Hot weather and altitude can reduce the performance of a generator
• Future-proofing – You may want to prepare for future energy needs
• Generator type – Different types of generators have different capabilities

Real-Life Applications and Benefits

Generator size calculators are useful to both homeowners and businesses. Homeowners can use a generator size calculator to select a backup power supply that can keep their essentials running during a power outage. Small businesses can use a generator size calculator to estimate the size of a backup generator for computers, lighting, air conditioning and other equipment.

Contractors can use a generator size calculator to estimate the power needs for their tools, while event planners can use a generator size calculator to provide electricity to stage lights and sound systems.

Generator size calculators can help you to avoid buying an unnecessarily large generator, which costs more and produces more emissions. You can also avoid buying a too small generator, which would not be able to power your essential appliances.

Accuracy, Assumptions, and Limitations

The accuracy of a generator size calculator depends on the accuracy of the information you provide. If the information on your appliances is outdated or incorrect, the calculator will produce faulty results.

The calculator also assumes that you have a fundamental understanding of generators and their capabilities.

The calculator does not account for the fact that certain types of equipment, such as air conditioners, water pumps and industrial compressors, have complex starting characteristics.

The calculator also does not account for the fact that three-phase equipment and some electronics require special consideration.

Generator Size Calculator FAQs

1. How do I know what size generator I need for my house?

It depends on the appliances you want to power with a generator. A generator for lights, fans and a refrigerator will be significantly smaller than a generator for air conditioning, water pumps and other household appliances.

2. How many watts does a refrigerator require?

A refrigerator can consume between 100 and 800 watts of electricity, depending on its size and energy efficiency.

3. What’s the difference between running watts and starting watts?

Running watts refer to the amount of power an appliance needs to stay on. Starting watts refer to the amount of power an appliance needs to turn on. The difference between the two depends on how the manufacturer specifies the starting watts.

4. Should I add a safety margin when calculating generator size?

Yes, it’s a good idea to add a safety margin, especially if you are not certain about the requirements of your appliances or equipment. A reasonable safety margin is between 10 and 25 percent, depending on your needs.

5. How do I convert generator watts to kilowatts?

You divide watts by 1,000. For example, 5,000 watts would be equal to 5 kilowatts (kW).

6. Is a higher kW generator always better?

Not necessarily. A higher kW generator will be larger and more expensive, and it will consume more fuel. Make sure to choose a generator that can meet your requirements without unnecessary expenses.

7. Can I use a generator size calculator to determine the exact size of a generator?

No, not really. You should always double-check the information you entered into the calculator and consult an electrician for complex requirements or permanent generator installation.