To determine the size of generator you need, calculate the total power output of the equipment you want to run, taking into account the starting wattage, and convert this to kilowatts (kW)
. Ensure the generator can supply slightly more power than your maximum requirements
. Here's how to calculate the size of a generator:
- List all items you want the generator to power Missing even a few items could lead to under-sizing, which can result in power shortages
- Find the starting and running wattage of each item Check the owner's manual, look up the model number online, or check the equipment's identification plate
- Calculate the total power requirement for all items Total the power requirements using kilowatts (kW)
. If your equipment lists power usage in amperes, convert it to watts
. The formula for this is Volts x Amps = Watts
- Account for surge wattage Motor-driven appliances experience a surge in wattage for a few seconds
. To calculate surge wattage, use the formula: Total surge wattage = Running wattage of the appliances + Single highest starting watts out of the items you want to use
- Convert kW to kVA Generators are rated in kilo-volt-amperes (kVA), which measures the total power in use in a system
. In a 100% efficient system, kW = kVA
. Because electrical appliances are not 100% efficient, a 4000W generator might not fulfill your 4000W power requirements
- Add a safety margin Divide the total watts by 1000 to find kilowatts and add a 20% safety margin
. This final number is your minimum Generator Capacity requirement
Different size generators and their common uses
:
- 500 to 3,000 watts: Recreation, power tools, small appliances, lights
- 3,100 to 6,000 watts: Recreation, heating and cooling, mid-size appliances
- 5,000 to 10,000 watts: For small to medium homes, this should be sufficient
- 6,100 to 10,000 watts: Emergency power, heating and cooling, large appliances, water heaters
- 10,000 and 12,000 watts: An emergency backup power system
- 10,100 watts and above: Emergency power and whole home
- 15,000 watts: A powerful system to run a small home
- 20,000 watts: For large homes, you may need a generator rated at 20,000 watts or more to cover your entire energy consumption
- 25,000 watts: A mini-power plant that can run a small to mid-sized home or business
- 30,000 watts and up: A mini-power plant that can run a mid-sized to large home or business
You can use online generator sizing calculators to estimate what size generator you need
. However, these only provide a very rough estimate
