Electrical Load Calculator

How to Use the Electrical Load Calculator

Sizing your electrical service correctly is essential for safety and code compliance. This calculator follows the National Electrical Code (NEC) standard method for residential load calculations. Enter your home's total square footage, select your major appliances, and specify the air conditioning tonnage. The calculator applies NEC demand factors to produce a realistic estimate of your total electrical load and recommends the appropriate panel size.

General lighting is calculated at 3 watts per square foot, which covers all lighting and general-use receptacles. The NEC adds a fixed 3,000 watts for small appliance circuits (kitchen, dining room, and pantry) and 1,500 watts for the laundry circuit. A demand factor is applied to this general load: the first 3,000 watts at 100% and the remainder at 35%, reflecting the reality that not all lights and outlets are used simultaneously.

Major Appliance Loads

Electric ranges are rated at 8,000 watts, which is the NEC standard demand for a single household cooking appliance. Electric dryers draw approximately 5,000 watts. Electric water heaters are typically rated at 4,500 watts. These loads are added at full value because they represent dedicated high-draw circuits. For heating and cooling, the calculator uses the larger of air conditioning (3,517 watts per ton) or electric heat (10 watts per square foot), since these systems never operate at the same time.

Understanding Panel Sizing

The total load in watts is divided by 240 volts to determine the amperage. Panel sizes come in standard increments: 100A, 150A, 200A, and 400A. A 200-amp panel is the most common for modern homes and accommodates most configurations up to about 3,000 square feet with central AC and standard electric appliances. Homes that are all-electric (electric heat, range, dryer, and water heater) in cold climates often require a 200-amp panel even at moderate sizes. Very large homes or those with workshops, pools, or hot tubs may need 400-amp service.

Electrical Safety Tips

Always hire a licensed electrician for panel upgrades and major electrical work. Obtain the required permits before starting work, as unpermitted electrical modifications can void insurance and create safety hazards. When adding circuits, ensure the total load does not exceed 80% of the panel's rated capacity, which is the NEC continuous load requirement. Label every circuit breaker clearly and keep an up-to-date panel schedule. Install AFCI (Arc-Fault Circuit Interrupter) breakers on bedroom circuits and GFCI protection in kitchens, bathrooms, garages, and outdoor areas as required by current code.

Frequently Asked Questions

How do I calculate electrical load for my house?

Start with general lighting at 3 watts per square foot. Add 3,000W for small appliance circuits and 1,500W for laundry. Apply the NEC demand factor: first 3,000W at 100%, remainder at 35%. Then add major appliances and the larger of AC or electric heat. Divide total watts by 240V for amperage.

What size electrical panel do I need?

Panel size is based on total calculated amperage at 240 volts. Up to 100 amps requires a 100A panel. 101-150 amps needs a 150A panel. 151-200 amps requires a 200A panel. Over 200 amps requires a 400A panel or dual panels.

Why do I use the larger of AC or heat, not both?

The NEC recognizes that air conditioning and electric heating are never used simultaneously. Since they operate in different seasons, the load calculation uses only the larger of the two values. This prevents oversizing the panel and service entrance.

What is the NEC demand factor?

The NEC demand factor accounts for the fact that not all lights and receptacles are used at the same time. The first 3,000 watts is calculated at 100%, and everything above 3,000 watts is reduced to 35%. This gives a realistic estimate of actual peak demand.

Is a 200-amp panel enough for most homes?

Yes. A 200-amp panel is sufficient for most single-family homes up to about 3,000 square feet with standard electric appliances and central AC up to 5 tons. Homes with all-electric systems in cold climates or homes over 4,000 square feet may need 400-amp service.