Home Generator Size Calculator
Use this calculator to estimate the appropriate generator size (in Watts and kVA) needed to power your essential home appliances during an outage. Select the appliances you plan to run simultaneously and specify their quantities.
Select Appliances and Quantities:
Recommended Generator Size:
Recommended Running Watts: 0 W
Recommended Starting Watts (Surge): 0 W
Recommended Running kVA: 0.00 kVA
Recommended Starting kVA (Surge): 0.00 kVA
Note: kVA is calculated assuming a power factor of 0.8.
Understanding Generator Sizing for Your Home
Choosing the right size generator for your home is crucial for ensuring you have reliable power during outages without overspending or underpowering your essential appliances. An undersized generator won't be able to handle your load, leading to frustrating power interruptions, while an oversized one will consume more fuel and cost more upfront than necessary.
Running Watts vs. Starting Watts (Surge Power)
When sizing a generator, it's vital to understand the difference between running watts and starting watts:
- Running Watts (Rated Watts): This is the continuous power an appliance needs to operate once it's started. Your generator's continuous power output must meet or exceed the sum of the running watts of all appliances you want to run simultaneously.
- Starting Watts (Surge Watts): Many motor-driven appliances (like refrigerators, air conditioners, well pumps, and sump pumps) require a brief burst of extra power to start up. This momentary surge can be 2-3 times their running wattage. Your generator must be able to provide this surge power for the largest motor-driven appliance you intend to start while other appliances are already running.
Our calculator takes both these factors into account to give you a realistic estimate of the generator's required running and starting capacities.
How to Use This Calculator
- Identify Essential Appliances: Go through the list and select all the appliances you absolutely need to run during a power outage.
- Specify Quantities: For each selected appliance, enter the number of units you have.
- Click "Calculate": The calculator will sum up the running watts for all selected items and determine the maximum starting surge required by any single motor-driven appliance.
- Review Results: You'll get a recommendation for both the continuous running watts and the peak starting watts your generator should be capable of. Results are also provided in kVA (kilovolt-amperes), a common rating for larger generators, assuming a typical power factor of 0.8.
Factors Beyond the Calculator
While this calculator provides a solid starting point, consider these additional factors:
- Future Needs: Are you planning to add more appliances in the future? It might be wise to slightly oversize your generator to accommodate growth.
- Fuel Type: Generators run on gasoline, propane, natural gas, or diesel. Consider availability, storage, and cost of fuel in your area.
- Noise Level: Generators can be noisy. If it's for residential use, look for models with lower decibel ratings, especially if it will be close to your home or neighbors.
- Installation: Portable generators are manually connected, while standby generators are permanently installed and automatically turn on when power is lost. Each has different installation requirements and costs.
- Power Factor: Our kVA calculation uses a common power factor of 0.8. Actual power factors can vary depending on your specific load, but 0.8 is a good general estimate for typical residential loads.
- Safety: Always operate generators outdoors in a well-ventilated area, far away from windows and doors, to prevent carbon monoxide poisoning. Never backfeed power into your home's electrical system without a proper transfer switch installed by a qualified electrician.
Always consult with a qualified electrician or generator professional to confirm your specific needs and ensure safe installation.
';
html += ";
html += '';
html += ";
html += '(Run: ' + appliance.running + 'W, Start: ' + appliance.starting + 'W)';
html += '
';
}
container.innerHTML = html;
}
// Call this function to generate inputs when the page loads
window.onload = generateApplianceInputs;
function calculateGeneratorSize() {
var totalRunningWatts = 0;
var maxSurgeDifference = 0; // This is (starting – running) for the single largest surge appliance
for (var i = 0; i 0) {
totalRunningWatts += quantity * appliance.running;
// Calculate surge difference for this appliance
// We only care about the largest single surge, not sum of all surges
var currentSurgeDifference = appliance.starting – appliance.running;
if (currentSurgeDifference > maxSurgeDifference) {
maxSurgeDifference = currentSurgeDifference;
}
}
}
}
var recommendedRunningWatts = totalRunningWatts;
var recommendedStartingWatts = totalRunningWatts + maxSurgeDifference;
// Power factor for kVA calculation (common for residential loads)
var powerFactor = 0.8;
var recommendedRunningKVA = (recommendedRunningWatts / 1000 / powerFactor).toFixed(2);
var recommendedStartingKVA = (recommendedStartingWatts / 1000 / powerFactor).toFixed(2);
document.getElementById('outputRunningWatts').innerText = recommendedRunningWatts;
document.getElementById('outputStartingWatts').innerText = recommendedStartingWatts;
document.getElementById('outputRunningKVA').innerText = recommendedRunningKVA;
document.getElementById('outputStartingKVA').innerText = recommendedStartingKVA;
document.getElementById('result').style.display = 'block';
}