Electrical Load Calculator for House

To size a home's electrical service, total the connected load in volt-amps, apply the NEC demand factors, and divide by 240 volts. A 2,000 sq ft home with 15,000 VA of fixed appliances has a total connected load of 25,500 VA. Applying the standard demand (first 10,000 VA at 100%, the rest at 40%) gives 16,200 VA of demand, or 67.5 amps at 240V — comfortably served by a 100-amp service. Most modern homes are built with 200A service to leave room for EV charging, heat pumps, and future loads.

A load calculation is required whenever you install a new service, upgrade a panel, or add a large load like an EV charger. It proves the service and main breaker will not be overloaded. This calculator uses a simplified version of the NEC Article 220 standard method; a licensed electrician performs the full calculation for permits, but this gives you an accurate planning estimate.

The standard method builds up the load from fixed pieces, then discounts it with demand factors because not everything runs at once:

Here is what each term represents:

• General lighting load at 3 VA per square foot covers all the lighting and general-use receptacles. A 2,000 sq ft home contributes 6,000 VA here.
• Small-appliance circuits — the code requires at least two 20A kitchen circuits, each counted at 1,500 VA, for 3,000 VA.
• Laundry circuit adds a fixed 1,500 VA.
• Fixed appliances — water heater, dishwasher, disposal, HVAC, range, dryer — are summed as nameplate VA.
• Demand factor — the first 10 kVA of the general load is counted fully; the remainder is discounted to 40% because a household never runs every circuit simultaneously.

After the demand load is found, dividing by 240V gives the service current. Individual circuits within the panel are then sized with the breaker size calculator and the wire size calculator.

Example 1 — 2,000 sq ft home, 15,000 VA of appliances: General lighting = 3 × 2,000 = 6,000 VA. Small appliance = 3,000 VA. Laundry = 1,500 VA. Subtotal general = 10,500 VA. Add appliances: 10,500 + 15,000 = 25,500 VA connected. Demand = 10,000 + (15,500 × 0.4) = 10,000 + 6,200 = 16,200 VA. Amps = 16,200 ÷ 240 = 67.5 A → 100A service.

Example 2 — 3,000 sq ft all-electric home: General lighting = 9,000 VA, small appliance 3,000, laundry 1,500 → 13,500 VA. Add 40,000 VA of appliances (electric range, dryer, water heater, heat pump). Connected = 53,500 VA. Demand = 10,000 + (43,500 × 0.4) = 10,000 + 17,400 = 27,400 VA. Amps = 27,400 ÷ 240 = 114 A → 125A service, though most builders would specify 200A for headroom.

Example 3 — small 1,200 sq ft cottage: General lighting = 3,600 VA, small appliance 3,000, laundry 1,500 → 8,100 VA. Add 6,000 VA of appliances. Connected = 14,100 VA. Demand = 10,000 + (4,100 × 0.4) = 11,640 VA. Amps = 48.5 A → a 100A service is the practical minimum (60A services are rarely installed today).

Residential services come in standard sizes. Picking the right one balances present demand against future growth.

100A service suits a small to mid-size home with gas heat, gas water heating, and modest electric loads. It is the practical minimum for a modern dwelling. 125A and 150A services bridge homes that have one or two large electric loads (a heat pump or electric range) but not everything electric. 200A service is the modern default for new construction and is strongly recommended if you plan to add EV charging, electric heat, a heat pump water heater, or a solar/battery system. A 200A panel also provides more breaker spaces for future circuits.

If your calculated demand is close to a service boundary, choose the larger size — service upgrades are expensive to do later, and electrification trends (EVs, heat pumps, induction cooking) keep pushing household demand up. When adding a single large load to an existing panel, run this calculation with the new appliance included to confirm the main breaker and service still have capacity; otherwise a load-management device or service upgrade may be needed.

1. Enter the finished floor area in square feet. Include heated living space; the code uses this for the general lighting load. Do not include open porches or unfinished areas.
2. Total your fixed appliances in VA. Add the nameplate volt-amps (or watts) of the water heater, HVAC, electric range, dryer, dishwasher, disposal, and any other permanently connected appliance. Enter the sum.
3. Read the recommended service size. The primary result rounds the calculated current up to the next standard service. The secondary outputs show total connected load, demand load after diversity, and the calculated current in amps.

This simplified tool omits some refinements of the full NEC calculation — such as the larger of heating vs cooling, the 8 kW+ range demand table, and the optional method in NEC 220.82. For a permit-ready calculation, have a licensed electrician run the complete Article 220 analysis. Size individual circuits with the circuit load calculator.

• Adding heating and cooling together. The NEC lets you count only the larger of the two, since they never run at the same time. Double-counting inflates the service size.
• Skipping the demand factors. Summing every nameplate at 100% overstates demand badly; the whole point of the standard method is that loads are diverse.
• Forgetting future loads. An EV charger can add 7,200–11,520 VA of continuous demand. Size the service for what you will add, not just what exists.
• Using watts and VA interchangeably for motors. Motor and HVAC loads have a power factor below 1, so their VA exceeds their watts. Use nameplate VA where available.
• Ignoring the 83% rule for feeders. Certain dwelling feeders and services can use a reduced conductor size per NEC 310.12; a professional applies these correctly.

The NEC actually offers two ways to calculate a dwelling's service load, and knowing the difference helps you interpret this calculator's result. The standard method of Article 220 Part III — the one this tool uses — builds the load from individual components (general lighting at 3 VA per square foot, small-appliance and laundry circuits, and each fixed appliance) and then applies demand factors piece by piece. It is the more granular, traditional approach and is required in commercial work and many mixed situations.

The optional method of NEC 220.82 is a simplified alternative available for a single dwelling unit. It sums the general loads and every appliance at 100%, then applies a single blanket demand factor: the first 10 kVA at 100% and everything above 10 kVA at only 40%. Heating and air conditioning are handled with their own separate factors, taking the largest applicable value. For a typical all-electric home, the optional method usually yields a smaller — and often more realistic — service size than the standard method, because its demand factor is more aggressive. That is why a house that calculates to 150A by the standard method might qualify for 125A under the optional method.

Neither method is "wrong"; the code permits both for dwellings, and an electrician will often run both and choose the one that best fits the situation and the local inspector's expectations. This calculator deliberately uses the standard-method logic with a 40% demand on the load above 10 kVA, which produces a sensible, slightly conservative planning number. Treat its output as a solid starting estimate rather than a permit document.

A few refinements neither this tool nor a quick estimate captures: electric ranges over 8 kW use the specific demand table in NEC 220.55 (a single 12 kW range counts as only 8 kW of demand, for instance); the largest motor in the system gets a 25% adder; and dwelling feeders and services may use the reduced-ampacity allowance of NEC 310.12. Each of these tends to lower the final number, which is another reason a professional calculation frequently permits a smaller service than a naive sum of nameplates would suggest. When the stakes are a service upgrade costing thousands of dollars, having a licensed electrician run both methods is well worth it.

A house load calculation is not just a formality — it is required by code and by common sense in several situations.

New construction and service upgrades always require a load calculation to size the service entrance conductors and main breaker. Adding a large load — an EV charger, heat pump, hot tub, electric range, or ADU — requires confirming the existing service can carry the new demand. Solar and battery installations trigger the busbar and 120% rule calculations, which start from the service size. Selling or insuring an older home with a 60A or 100A service may prompt an upgrade recommendation.

If the calculation shows you are near capacity, options include upgrading the service, installing an energy-management system that sheds loads, or choosing lower-demand appliances (a 40A EV charger instead of 60A, or a 120V Level 1 charger). Run the numbers here first, then confirm circuit-level sizing with the breaker size calculator and verify the main and feeders with a licensed electrician before pulling a permit.