Residential Load Calculation: NEC Standard Method
Chameera Sampath · 10/18/2026
Residential load calculation with the NEC 220 standard method: lighting VA, small-appliance circuits, demand factors, HVAC, a worked example and service size.
A residential load calculation estimates the largest load a house will place on its electrical service, so that the service, main panel and service conductors can be sized correctly. Under Article 220 of the National Electrical Code, the standard method totals lighting, receptacle and appliance loads and then applies demand factors, recognizing that not everything runs at full power at the same time.
Quick answer. General lighting at 3 VA per square foot, plus 1,500 VA for each small-appliance circuit (at least two) and 1,500 VA for laundry. Apply 100% to the first 3,000 VA and 35% to the next 117,000 VA. Add the range, dryer, fixed appliances (75% when there are four or more), the larger of heating or cooling, and 25% of the largest motor. Divide the total by 240 V to get the service current.
Why a load calculation is needed
A house's connected load, everything added up at nameplate, is far larger than the power it ever draws at once. Sizing a service on connected load would be wasteful; sizing it on guesswork risks an overloaded service. The load calculation applies code-defined demand factors to reach a figure that is safe and realistic. It is required for new services, service upgrades, and often when large loads such as an EV charger or heat pump are added.
The standard method step by step
| Step | Load | How it is counted |
|---|---|---|
| 1 | General lighting and receptacles | 3 VA × floor area in square feet (outside dimensions, habitable space) |
| 2 | Small-appliance circuits | 1,500 VA per kitchen/dining small-appliance circuit, minimum two |
| 3 | Laundry circuit | 1,500 VA |
| 4 | Demand factor on steps 1–3 | First 3,000 VA at 100%; 3,001 to 120,000 VA at 35%; remainder at 25% |
| 5 | Electric range | One range up to 12 kW: 8 kW demand; larger or multiple ranges per the code table |
| 6 | Electric dryer | 5,000 VA or nameplate, whichever is larger |
| 7 | Fixed appliances | Water heater, dishwasher, disposal and other fastened-in-place appliances: 100%, or 75% of the total when there are four or more |
| 8 | Heating and cooling | The larger of the two, since they do not run together |
| 9 | Largest motor | Add 25% of the largest motor's load |
| 10 | Service current | Total VA ÷ 240 V |
Worked example
A 2,000 square-foot house with an electric range, dryer, water heater and electric heat.
Lighting, small appliance and laundry
| Item | VA |
|---|---|
| General lighting: 2,000 ft² × 3 VA | 6,000 |
| Small-appliance circuits: 2 × 1,500 | 3,000 |
| Laundry | 1,500 |
| Subtotal | 10,500 |
| First 3,000 VA at 100% | 3,000 |
| Remaining 7,500 VA at 35% | 2,625 |
| Demand load | 5,625 |
Appliances and HVAC
| Item | Nameplate | Demand VA |
|---|---|---|
| Range (12 kW) | 12,000 | 8,000 |
| Dryer | 5,500 | 5,500 |
| Water heater | 4,500 | |
| Dishwasher | 1,200 | |
| Disposal | 900 | |
| Built-in microwave | 1,500 | |
| Four fixed appliances: 8,100 × 75% | 6,075 | |
| Electric heat 10 kW vs air conditioning 5 kVA: larger | 10,000 | |
| 25% of largest motor (disposal, 900 VA) | 225 |
Total: 5,625 + 8,000 + 5,500 + 6,075 + 10,000 + 225 = 35,425 VA
Service current: 35,425 ÷ 240 = 147.6 A
The calculated load fits a 150 A service at minimum. Many designers would choose 200 A to leave capacity for an EV charger, a heat pump or other future loads.
The optional method
Article 220 also provides an optional method for dwelling units, which applies a single demand percentage to most loads after the first 10 kVA. It often produces a lower figure than the standard method and is commonly used for existing houses and service upgrades. Either method is acceptable where its conditions are met; the authority having jurisdiction may specify which it expects.
Adding a load to an existing house
When adding an EV charger, heat pump or other large load, the question is whether the existing service has spare capacity. Approaches include:
- Recalculating the whole house with the new load included.
- Using a year of the utility's maximum demand data, where the code permits it for existing dwellings, plus 125% of the new load.
- Installing an energy management system that limits the total load, where permitted.
If the service is too small, the options are a service upgrade or a load-management device.
Sizing the conductors and breakers that follow
The load calculation sets the service rating. Each branch circuit is then sized separately: breaker ratings from the breaker size calculator, conductor ampacity from the ampacity calculator, and long feeders checked with the voltage drop calculator. For a backup supply, the generator sizing calculator uses running and starting loads instead. Once the circuits are installed, a panel schedule records each breaker, its connected load and the phase it is on; it lists loads but does not replace this calculation.
Common mistakes
- Counting heating and air conditioning together instead of taking the larger.
- Omitting the 25% largest-motor adder.
- Applying the 75% fixed-appliance factor with fewer than four appliances.
- Using the range nameplate instead of the demand value from the code table.
- Using a single-phase 240 V divisor for a three-phase service.
Frequently asked questions
How is a residential electrical load calculated? By the standard method in Article 220: lighting at 3 VA per square foot, small-appliance and laundry circuits at 1,500 VA each, demand factors, then appliances, the larger of heating or cooling, and 25% of the largest motor, divided by 240 V.
Is 100 A service enough for a house? It can be for a small house with gas heat, gas cooking and no large electric loads. A load calculation decides; houses with electric heat, an electric range and air conditioning usually need 150 A to 200 A.
What demand factor applies to lighting? For dwellings, the first 3,000 VA at 100%, the next 117,000 VA at 35%, and anything above that at 25%.
Do I need a load calculation to add an EV charger? Usually. An EV charger is a large continuous load, and the inspector will generally want to see that the existing service can carry it.
Scope
This guide summarizes the dwelling standard method in Article 220 of the National Electrical Code for single-family houses in the United States. Section numbers differ between code editions, and local amendments apply. Service sizing for permits should be prepared or reviewed by a licensed electrician.
Written by Chameera Sampath. Not yet reviewed by a licensed electrician — see the methodology page. To report an error, use the contact page.