Generator Load Calculator
Estimate how much generator power your appliances and equipment need before choosing a generator.
Select the appliances and equipment you want to run, adjust the quantities, and calculate your estimated running load, startup surge, and peak demand.
Generator Load Calculator
Select the equipment you expect to run together. We'll estimate your running load, startup surge and peak demand.
Add Your Appliances
Common U.S. loads are shown first. Use the nameplate or manufacturer data when available.
Demand Preview
Your estimate updates as you build your load. Click Calculate Load to review and confirm the demand.
How to Use the Generator Load Calculator
You don’t need to know every appliance’s wattage before you start. Choose the equipment you expect to run, and the calculator will use typical wattage estimates where available.
Choose Your Loads
Select the appliances or equipment you want your generator to power.
Common examples include:
You can adjust the quantity of each load or add a custom appliance when you have the manufacturer’s wattage information.
Review Your Demand
The calculator estimates three important numbers:
Running Load
The combined continuous wattage of the selected equipment.
Largest Startup Surge
The additional wattage required when the largest selected motor or compressor starts.
Estimated Peak Demand
Your running load plus the largest additional startup surge.
These numbers give you a starting point for determining the generator capacity you need.
Size Your Generator
Once your load is calculated, continue to the Generator Size Calculator.
Use the calculated running and startup requirements to compare generator specifications.
When shopping for a generator, check
Running Watts vs. Starting Watts
Understanding the difference between running and starting watts is important when sizing a generator.
Running Watts
Running watts are the power an appliance or piece of equipment normally uses while operating.
Example
Wattage
700 W
(running watts)
needed while running
Starting Watts
Some equipment uses additional power for a short period when its motor or compressor starts.
Common examples include:
Air conditioners
Refrigerators
Freezers
Well pumps
Sump pumps
Compressors
Power tools
Why Generator Load Matters
Choosing a generator based only on the largest appliance can lead to an undersized system.
For example, you might have:
Each load may seem small on its own, but their combined demand can be significant.
The calculator helps you look at the full group of loads you expect to operate, rather than guessing based on one appliance.
Example Generator Load Calculation
Suppose you want to operate:
Equipment |
Running Watts |
Additional Startup |
|---|---|---|
|
Refrigerator |
700 W |
2,200 W |
|
Sump Pump |
800 W |
1,300 W |
 LED Lights |
100 W |
0 W |
 Wi-Fi Router |
15 W |
0 W |
 TV |
120 W |
0 W |
1,735W
2,200W
3,935W
Compare the generator’s rated/running output, surge output, voltage, and your equipment’s actual requirements.
What About 120V and 240V Equipment?
Most household electronics and many appliances use 120V, while larger equipment such as some central air conditioners, well pumps, electric ranges, and other major equipment may require 240V.
If your load list includes 240V equipment, make sure the generator you choose provides compatible 120/240V output.
Wattage alone does not determine whether a generator can safely operate a particular appliance. Always check the equipment nameplate and the generator manufacturer’s specifications.
Most household appliances
and electronics typically
use 120V power.
Larger equipment may require 240V power and may have higher electrical demands.
If your load includes 240V equipment, make sure the generator supports the required voltage.
How Accurate Are the Wattage Estimates?
Based on average usage for common household items.
Aligned with manufacturer specifications where available.
Reflects common efficiency levels of modern appliances.
Based on equipment in good working condition.
Best for estimating short-term or intermittent use.
These estimates help you plan running and starting wattage from the equipment you select. For precise results, check the label or specifications on your actual equipment.
Important Starting-Demand Assumption
The calculator estimates peak demand using the largest additional startup surge from the selected loads. This is useful for a straightforward planning estimate, but it does not model every possible startup sequence. If multiple large motors or compressors can start at the same time, actual starting requirements may be higher. For large residential standby systems or complex installations, have a qualified professional verify generator capacity.
Select the equipment you want to run.
Choose common appliances, adjust quantities, or add your own equipment to build your generator load.
Account for motor and compressor startup.
Some equipment needs extra power when starting. We estimate the largest additional startup demand from your selected loads.
Use your demand to choose the right capacity.
Review your running and peak requirements, then continue to the Generator Size Calculator to determine what generator output to look for.
What Size Generator Do I Need?
Your load calculation is only the first step.
After calculating your demand, use our:
to determine the generator capacity you should look for.
When comparing generators, check:
The continuous power a generator can supply to run your appliances.
Extra power needed to start motors and high-demand appliances.
Make sure the voltage output matches your home or equipment needs.
Gasoline, propane, diesel, or dual fuel—choose what works best for you.
Ensure the generator is compatible with your transfer switch for safe and reliable backup power.
Always review the official specs and documentation for accurate information.
Don’t choose a generator based solely on a single peak-watt number.
Review the full specifications to ensure it meets your needs.
