TradesHow this works
The standard method adds a general load of 3 VA per square foot plus the small-appliance and laundry circuits, then applies the Table 220.42 demand factor. It adds the range, the dryer, the fixed appliances, and the larger of heating or cooling, each with its own rule. The total in volt-amps divided by the service voltage gives the calculated current, and the tool rounds up to the next standard service size.
This is a Tier 3 planning estimate. It is a fast way to check whether a 100, 150, or 200 amp service fits and to see what is driving the load. The official calculation for a permit belongs to a licensed electrician and the authority having jurisdiction.
Common questions
Is this an official load calculation?
No. It is a planning estimate to sanity-check a service size. The official calculation for a permit has to be done and signed by a licensed electrician, and the authority having jurisdiction reviews it. Use this to get in the ballpark and to understand what drives the number.
What is the difference between the standard and optional methods?
This tool uses the Article 220 standard method, which applies a demand factor to the general lighting and adds the appliances with their own demand rules. The optional method under 220.83 uses a single overall demand factor and usually gives a smaller service. If your result is near a size boundary, run the optional method too.
Why do heat and air conditioning not both count?
NEC 220.60 lets you use the larger of the two, since a house does not heat and cool at the same time. In a cold climate with electric heat, heating usually wins and can push the service up a size.
Sources: NEC Article 220 Part III standard method: 220.12, 220.42, 220.53, 220.54, 220.55, 220.60 (2023). Engine version 1.0.0. Risk tier 3.