NEC Load Calculation

Size a dwelling service with the NEC Article 220 standard method — lighting, range, dryer and HVAC demand factors applied, every line shown.

How to use it

Work down the form with the plans or the nameplates in front of you — every field maps to one line of Article 220.

Living area is the habitable square footage figured per 220.12: outside dimensions, not counting open porches, garages, or unfinished spaces that are not adaptable for future use. Small-appliance circuits are the 20 A kitchen and dining receptacle circuits — 220.52(A) requires at least two, and the calculator holds you to that. Laundry circuit is the 220.52(B) receptacle circuit, minimum one. Each of these counts at 1500 VA.

Range takes the nameplate in kW; enter 0 for a gas range. Dryer takes nameplate VA, with the 220.54 floor of 5000 VA applied automatically; 0 for gas. Fixed appliances are the fastened-in-place items — dishwasher, disposal, water heater, built-in microwave, attic fan — totaled by nameplate, with a separate count field because the 75% demand factor of 220.53 turns on at four or more. Do not put the range, dryer, or HVAC in this bucket; they have their own lines. Heat or A/C takes the larger of the two only, per 220.60 — they never run at once, so only the bigger one counts.

The method — and which method this is

This is the standard (long-form) method of Article 220, Part III. The NEC also permits an Optional Method under 220.82 for single dwellings on services of 100 A or more — a different calculation with different demand factors that often lands smaller. This calculator does not compute the optional method, and neither does the app. If your jurisdiction or your customer wants 220.82, run 220.82; do not compare its answer to this one and assume something is broken.

The standard method builds the load in five pieces:

1. General lighting — area × 3 VA/ft², plus 1500 VA per small-appliance and laundry circuit, then the 220.42 demand tiers: first 3000 VA at 100%, 3001–120,000 VA at 35%, anything beyond at 25%.
2. Range — Table 220.55 Column C: one range at 12 kW or less counts 8000 VA regardless of nameplate. Over 12 kW, the 8000 grows by 5% per kW over 12. Note 1 to the table words the step as “per kW or major fraction”; both this calculator and the app round any fraction up, so a 12.1 kW range is treated as one full kW over. That is deliberately conservative — it sizes slightly high rather than slightly low — but it is our rounding, not the table’s wording, and a strict reading of Note 1 would leave 12.1 kW at 8,000 VA.
3. Dryer — 5000 VA or nameplate, whichever is larger (220.54).
4. Fixed appliances — the nameplate total at 100%, or at 75% when there are four or more of them (220.53).
5. Heat or A/C — the larger, at 100% (220.60).

Sum the five, divide by 240 V, and take the smallest standard service rating at or above the result. Above 600 A the tool refuses rather than answering — the largest standard service is 600 A, and a load past it is an engineering job, not a table lookup.

Worked example

The calculator’s defaults: a 2,000 ft² all-electric house with a 12 kW range, a 5000 VA dryer, four fixed appliances totaling 8100 VA (dishwasher 1200, disposal 900, microwave 1500, water heater 4500), and 10 kW of electric heat against a smaller A/C.

General: 2,000 × 3 = 6,000 VA, plus two small-appliance circuits and one laundry circuit at 1500 VA each — 10,500 VA connected. Apply 220.42: 3,000 at 100% plus 7,500 at 35% = 5,625 VA. Range at 12 kW: 8,000 VA. Dryer: 5,000 VA. Fixed appliances: four of them, so 8,100 × 75% = 6,075 VA. Heat: 10,000 VA.

Total: 5,625 + 8,000 + 5,000 + 6,075 + 10,000 = 34,700 VA. Divide by 240 V: 144.58 A. The smallest standard service at or above that is 150 A — though most builders would land a 200 A panel here for the headroom, and nothing in the code stops them. The calculation sets the floor, not the choice.

Where it goes wrong in the field

Adding heat and A/C together. 220.60 exists because they are noncoincident — entering the sum instead of the larger inflates the service a full size on most houses. The reverse mistake is entering the A/C because it was the number on the permit, when the heat strips are bigger.

Double-counting appliances. The range, the dryer, and the HVAC each have their own line. Put any of them in the fixed-appliance total too and the load is counted twice — an error that survives review precisely because every individual number looks right.

Gross square footage. Counting the garage and the open porch adds phantom lighting load. It rarely changes the service size on its own, but stacked on other padding it does, and an inspector who checks the area against 220.12 will re-run everything else too.

Forgetting what is not in here. The number this page produces is the minimum ampacity for the ungrounded service conductors. The neutral is sized separately under 220.61 and is usually smaller; an EV charger added next year under 220.57 is load this calculation never saw. If an EVSE is on the horizon, run the calculation with it included before committing to a service size — 7,200 VA is 30 A of service at 240 V, and it is the difference between a 150 A and a 200 A answer on exactly the house in the example above.

Code references

• NEC 220.12General lighting load — 3 VA per ft² of dwelling living area2023 edition
• NEC 220.52Small-appliance (min 2) and laundry (min 1) branch circuits at 1500 VA each2023 edition
• NEC 220.42General lighting demand — first 3000 VA at 100%, 3001–120,000 at 35%, remainder at 25%2023 edition
• NEC 220.55Household range demand — Table 220.55 Column C, one range 12 kW or less at 8 kW2023 edition
• NEC 220.54Electric clothes dryer — 5000 VA or nameplate, whichever is larger2023 edition
• NEC 220.53Four or more fastened-in-place appliances at 75% demand2023 edition
• NEC 220.60Noncoincident loads — larger of heating or A/C only2023 edition

Section numbers and table values move between editions, and jurisdictions amend them. Confirm against the edition your authority having jurisdiction enforces.

Common questions

What size electrical service do I need?

Whatever the calculated load says, not what the neighbor's house has. Run the Article 220 standard method — general lighting at 3 VA/ft², the required small-appliance and laundry circuits, then range, dryer, fixed appliances and the larger of heat or A/C, each at its demand factor — divide the total VA by 240, and take the next standard service size up. A typical 2,000 ft² all-electric house lands around 145 A, which means a 150 A service minimum and a 200 A service in practice.

How do I calculate residential electrical load?

Standard method, in order. Multiply living area by 3 VA/ft², add 1500 VA per small-appliance circuit (minimum two) and per laundry circuit (minimum one), then apply the 220.42 demand tiers — first 3000 VA at 100%, the rest to 120,000 VA at 35%. Add the range from Table 220.55 Column C, the dryer at 5000 VA or nameplate, fixed appliances at 75% if there are four or more, and the larger of heating or A/C. Divide by 240 V for amps.

Is square footage enough to size a 200 amp service?

No — square footage is the smallest part of the load. At 3 VA/ft², even 4,000 ft² of floor is only 12,000 VA before demand factors. What actually drives a house to 200 A is the equipment list — electric range, dryer, water heater, and above all electric heat. A small all-electric house can need 200 A while a large gas-served one calculates comfortably under 100 A.

What is the difference between the NEC standard and optional method?

The standard method (Part III) applies a separate demand factor to each load category, the way this calculator does. The optional method of 220.82, allowed for a single dwelling with a service of 100 A or more, lumps most loads together at 100% for the first 10 kVA and 40% for the rest, and usually produces a smaller number. Both are code-legal where permitted; they just answer differently. This tool computes only the standard method.

For the method behind this — worked examples, the tables, and where it goes wrong — read the full guide.