Free Electrical Load Calculator Online
Total electrical load, recommended breaker size for home appliances
The Electrical Load Calculator totals the wattage of appliances on a circuit or in a property, converts the result to amperage at your supply voltage, and recommends the minimum breaker size to run safely without tripping. Electricians sizing new panels, homeowners adding circuits, and engineers planning building services use it to ensure circuits are neither undersized nor wastefully oversized.
Frequently Asked Questions
About the Electrical Load Calculator
Every electrical circuit has a rated capacity, and the National Electrical Code (NEC) and equivalent standards require that circuits be sized so that the calculated load does not exceed 80% of the breaker rating โ the "80% derate rule." Overloading a circuit doesn't just trip the breaker; chronic overloads generate heat in wiring, degrading insulation over time and creating a fire risk.
This calculator adds up the wattage of all appliances on a circuit, converts to amperage at the supply voltage (120 V in North America, 230โ240 V in Europe and the UK, 415 V for three-phase), and then applies the 80% derate to give the minimum safe breaker rating. It flags when existing circuits are at or near capacity.
For whole-house load calculations used to size a main service panel, sum all individual circuit loads and apply a demand factor (not all circuits run at full load simultaneously). This tool handles the per-circuit calculation; for panel sizing, work with a licensed electrician who will also account for future load growth and local code requirements.
Formula Used
Total Load (Watts) = ฮฃ(Appliance Wattage ร Daily Hours)
Amperage = Watts / Voltage
When Should You Use This?
The Electrical Load Calculator is ideally suited for contractors, builders, architects, and DIY enthusiasts who need to perform quick, accurate calculations related to general calculations. Use this tool when you need to verify figures, compare different scenarios, or get a precise answer without manual computation errors.
What Does The Result Mean?
The calculated output provides an instant, accurate resolution to your input parameters. You can use these results directly for your planning, assignments, or professional tasks, knowing they are based on standardized formulas.
Example Calculation
Calculating load for a kitchen circuit at 240 V
๐ฅ Inputs
- Refrigerator: 150 W
- Microwave: 1,200 W
- Dishwasher: 1,800 W
- Electric kettle: 2,000 W
- Supply voltage: 240 V
๐ข Calculation Steps
- 1Total wattage: 150 + 1,200 + 1,800 + 2,000 = 5,150 W
- 2Note: kettle and microwave rarely run simultaneously; peak load โ 3,950 W
- 3Peak amperage: 3,950 รท 240 = 16.5 A
- 4Apply 80% NEC derate: required breaker capacity = 16.5 รท 0.80 = 20.6 A
- 5Next standard breaker size: 25 A (or 20 A if staggering appliance use)
Limitations of this Calculator
- Results are based purely on the mathematical relationship of the inputs provided.
- Does not account for edge cases or extreme outlier values that fall outside standard formula constraints.
- Calculated outputs should be double-checked against your specific real-world requirements before finalizing important decisions.
How to Use the Electrical Load Calculator
- 1Enter your values into the Electrical Load Calculator input fields above.
- 2Review the input labels to ensure you are using the correct units.
- 3Click the "Calculate" button to get your instant result.
- 4Use the step-by-step breakdown to understand how the result was calculated.
- 5Export or copy your result to use in reports or share with others.
Tips & Best Practices
- Double-check your input units before calculating โ using the wrong unit is the most common source of errors.
- Bookmark this Electrical Load Calculator for quick access next time you need it.
- Use the share button to send your results to a colleague or save them for later reference.
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