240V (Standard US Split-Phase)
120V (Single Circuit)
208V (Commercial)
Calculation Results
Total Estimated Wattage:0 W
Calculated Amperage:0 A
Recommended Minimum Service/Breaker (125% Safety Factor):0 A
function calculateLoad() {
var sqFt = parseFloat(document.getElementById('sqFt').value) || 0;
var smallAppCircs = parseFloat(document.getElementById('smallApplianceCircuits').value) || 0;
var range = parseFloat(document.getElementById('rangeWatts').value) || 0;
var dryer = parseFloat(document.getElementById('dryerWatts').value) || 0;
var waterHeater = parseFloat(document.getElementById('waterHeaterWatts').value) || 0;
var hvac = parseFloat(document.getElementById('hvacWatts').value) || 0;
var laundry = parseFloat(document.getElementById('laundryCircuit').value) || 0;
var voltage = parseFloat(document.getElementById('systemVoltage').value) || 240;
// General Lighting Load (3 Watts per sq ft per NEC)
var generalLoad = sqFt * 3;
// Small appliance loads (1500 Watts per circuit)
var smallAppLoad = smallAppCircs * 1500;
// Simple sum for general estimation
// Note: Professional NEC calculations use demand factors (e.g., first 3000VA at 100%, etc.)
// This calculator provides a conservative total load estimation.
var totalWatts = generalLoad + smallAppLoad + range + dryer + waterHeater + hvac + laundry;
var totalAmps = totalWatts / voltage;
var safetyAmps = totalAmps * 1.25;
document.getElementById('resWatts').innerHTML = Math.round(totalWatts).toLocaleString() + " W";
document.getElementById('resAmps').innerHTML = totalAmps.toFixed(2) + " A";
document.getElementById('resSafety').innerHTML = Math.ceil(safetyAmps) + " A";
document.getElementById('loadResults').style.display = 'block';
}
Understanding Residential Electrical Load
An Electrical Load Calculator is an essential tool for homeowners, DIYers, and electricians to estimate the total demand placed on an electrical system. Whether you are adding a new hot tub, finishing a basement, or upgrading your main service panel, knowing your total wattage and amperage is critical for safety and compliance with the National Electrical Code (NEC).
How Electrical Load is Calculated
The calculation is based on the sum of several different types of loads within a building:
General Lighting & Receptacles: Typically calculated at 3 Watts (VA) per square foot of living space.
Small Appliance Branch Circuits: The NEC requires at least two 20-amp circuits for kitchen small appliances, valued at 1,500 Watts each.
Laundry Circuit: A dedicated 20-amp circuit valued at 1,500 Watts.
Fixed Appliances: Heavy-duty equipment like electric ranges, clothes dryers, water heaters, and HVAC systems have specific wattage ratings found on their nameplates.
The Importance of the 125% Rule
Electrical codes often require that a circuit breaker or service panel be sized for 125% of the continuous load. This "safety factor" prevents the breaker from overheating and nuisance tripping during extended periods of use. For example, if your calculated load is 80 Amps, a 100-Amp service is the minimum recommended size.
Example Calculation
Imagine a 2,000 sq. ft. home with the following features:
General Lighting: 2,000 sq. ft. × 3W = 6,000W
Small Appliances (2): 3,000W
Laundry: 1,500W
Water Heater: 4,500W
Range: 8,000W
Total: 23,000 Watts
At 240 Volts, the amperage is 95.83 Amps (23,000 / 240). Applying the 125% safety factor (95.83 × 1.25) results in 119.79 Amps, suggesting a 125A or 150A panel would be appropriate.
Note: This calculator provides a general estimation. Official load calculations for permit applications should be performed by a licensed electrician or based on the specific demand factor tables in the NEC Article 220.