A residential electrical load calculator uses NEC Article 220 demand factors to determine the minimum electrical service size your home needs. By accounting for general lighting at 3 VA/sq ft, small appliance circuits, laundry, and major appliances — then applying 100% to the first 10 kVA and 40% to the remainder — it calculates the demand load that determines whether you need a 100A, 150A, 200A, or 400A service panel.
House Information
NEC uses 3 VA per sq ft for general lighting load
Each circuit = 1,500 VA (kitchen countertops, dining area)
Major Appliances
Check each appliance present in your home. Adjust wattages to match your actual equipment.
Service Panel Recommendation
NEC Article 220 Load Breakdown
| Load Item | Connected VA | Demand VA |
|---|
General lighting demand: 100% of first 10,000 VA, 40% of remainder. Major appliances added at nameplate or NEC demand value.
This is an estimate using the NEC Article 220 standard calculation. For permitted electrical work, always have a licensed electrician verify the load calculation and install or upgrade service equipment.
How to Use the Electrical Load Calculator
Before installing or upgrading an electrical service panel, electricians use a load calculation to determine the minimum service size required. This electrical load calculator follows NEC Article 220 — the same standard used by electricians across the United States — to help homeowners and contractors estimate whether a 100A, 150A, 200A, or 400A service is appropriate.
Step 1: Enter Your Living Area
Enter the total finished living area in square feet. NEC Article 220 requires a minimum general lighting load of 3 VA per square foot. This covers general-purpose lighting circuits and receptacle circuits throughout the home. Do not include unfinished basements, garages, or open porches unless they are conditioned and finished living spaces.
Step 2: Set Small Appliance and Laundry Circuits
The NEC requires a minimum of two 20-amp small appliance circuits (1,500 VA each) for kitchen counter areas. Most homes have exactly two, but kitchens with islands or large dining areas may have more. The laundry circuit (1,500 VA) is required in most residential occupancies per NEC 220.52. Together with the lighting load, these form the general load before demand factors are applied.
Step 3: Add Major Appliances
Check each major appliance installed in your home. The default wattages are typical nameplate values used in NEC load calculations: electric range at 8,000–12,000 W (NEC Table 220.55 applies specific demand factors for ranges over 12 kW), electric dryer at 5,500 W, water heater at 4,500 W, and HVAC at nameplate. For central air and electric heat, the NEC Article 220 requires using the larger of the two — you do not add both heating and cooling. Adjust any wattage to match your actual appliance nameplate.
Step 4: Review Your Demand Load and Service Size
The calculator applies NEC demand factors: 100% of the first 10,000 VA of the general load (lighting + small appliance + laundry), and 40% of anything over 10,000 VA. Major appliances are added at their full nameplate value. The total demand load is divided by 240V to determine the minimum service amperage, which is then rounded up to the nearest standard service size: 100A, 150A, 200A, or 400A.
Understanding the Results
The connected load is the theoretical sum of every load running simultaneously — rarely what actually happens. The demand load applies NEC's realistic diversity factor to produce the design figure. A service panel must be rated at or above the required amps. Many electricians recommend upgrading to the next size larger when you are near the threshold — for example, upgrading to a 200A panel when calculations show 175A — to leave room for future loads like an EV charger or added HVAC equipment.
FAQ
Is this electrical load calculator really free?
Yes, completely free with no account or signup required. All NEC Article 220 calculations run entirely in your browser. No square footage, appliance data, or results are ever sent to any server.
Is my data safe when using this tool?
Absolutely. Everything runs locally in your browser using JavaScript. No personal information is collected or transmitted. You can even use it offline once the page has loaded.
What is NEC Article 220?
NEC Article 220 is the section of the National Electrical Code that defines how to calculate residential and commercial electrical loads for the purpose of sizing service entrance equipment, conductors, and feeders. It uses demand factors — such as applying 100% to the first 10 kVA of lighting and appliance load, and only 40% to the remainder — to account for the fact that not all loads run simultaneously.
What is demand load versus connected load?
Connected load is the sum of the nameplate wattage of every electrical device in a home — as if everything were running at the same time. Demand load applies NEC demand factors to arrive at a more realistic figure that reflects actual simultaneous use. Service equipment is sized for the demand load, not the connected load.
What is the general lighting load of 3 VA per square foot?
NEC Article 220 requires a minimum general lighting load of 3 VA per square foot of living area. This covers general lighting circuits and general-purpose receptacle circuits. It is a planning minimum, not a measurement of actual lighting installed in the home.
Do I need a 200-amp or 400-amp service?
Most modern homes with standard appliances need a 200-amp service. You would typically need 320–400 amp service if you have a large home over 4,000 sq ft, multiple HVAC systems, an EV charger, a hot tub, a workshop with heavy equipment, or plan to add significant electric loads in the future. This calculator helps you determine which tier your home falls into.
How accurate is this compared to a licensed electrician's load calculation?
This tool follows the standard NEC Article 220 optional calculation method and gives a reliable estimate for planning and budgeting. A licensed electrician or electrical engineer may use additional detail — such as exact nameplate data, specific heat/AC demand rules, and local amendments — but the results from this calculator will be in the same ballpark. Always verify with a licensed electrician before purchasing service equipment.
Why does the NEC apply a 40% demand factor to loads over 10 kVA?
In a typical home, not all lights, outlets, and small appliances run at full load simultaneously. The NEC's demand factor (100% of the first 10 kVA, 40% of the rest) reflects this diversity of use. Major appliances like ranges, dryers, and HVAC systems are added separately with their own demand factors because they are more predictable and significant loads.