How this calculation works
The method builds a total, then discounts it. The discount is the whole point — nobody runs every load in a house at the same moment, and sizing for that would be absurd.
General lighting and receptacles
Three volt-amperes per square foot of habitable space, plus 1,500 VA for each required small-appliance branch circuit (minimum two), plus 1,500 VA for each laundry circuit. Square footage is measured from the outside dimensions and excludes open porches, garages and unfinished spaces not adaptable for future use.
The fixed loads
Range. Table 220.55 Column C takes a single household range rated 12 kW or less at 8,000 VA. A 12 kW range does not add 12,000 to your total; it adds 8,000. Ranges over 12 kW add 5% per additional kilowatt.
Dryer. 220.54 sets 5,000 VA or the nameplate, whichever is larger. There is no demand reduction for a single dryer.
Fastened appliances. Water heater, dishwasher, disposal, compactor and similar. 220.53 allows 75% of the total when there are four or more of them. Three or fewer and they go in at 100%.
Heating and cooling. 220.60 lets you drop the smaller of two loads that cannot operate at the same time. Electric heat and air conditioning are the classic pair — count only the larger.
Standard method versus optional method
220.82 offers an optional method for a single dwelling served by a single 120/240 volt set of service conductors rated 100 amps or greater. It takes the first 10 kVA at 100% and everything past it at 40%, which usually lands on a smaller service. Most residential work uses it.
Run both. Use whichever your AHJ accepts and your gear supports. And note the floor: 230.79(C) requires a minimum 100 amp service for a one-family dwelling regardless of what the math says.
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Frequently asked questions
Standard method or optional method?
The optional method in 220.82 is simpler and usually gives a smaller service, and it is permitted for a single dwelling with a single 120/240V service rated 100 amps or more. The standard method in Part III always works and is what exams test. Run both, submit whichever your AHJ prefers.
Does the garage count in the square footage?
No. The 3 VA per square foot applies to habitable space. Open porches, garages, and unused or unfinished spaces not adaptable for future use are excluded. A finished basement that could be living space is included.
Why is a 12 kW range only 8,000 VA?
Table 220.55 Column C is a demand table built on the observation that nobody runs every burner and the oven at full output at once. A single household range rated 12 kW or less is taken at 8,000 VA. Ranges over 12 kW add 5% to that figure per additional kilowatt.
What is the smallest service I can install on a house?
100 amps. 230.79(C) sets that as the minimum for a one-family dwelling, and it applies even when the calculated load comes out well under. Most new construction lands at 200 amps once you account for HVAC and any EV charging.
Do I have to include an EV charger?
Yes, and it is treated as a continuous load, so it goes in at 125%. Article 625 also permits an energy management system to limit the load instead of upsizing the service, which is increasingly how retrofits get done on older 100 and 150 amp panels.
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