Residential Load Calculation — NEC Article 220
Enter floor area, appliances, HVAC, and EV charger loads — get the required service ampacity using the NEC Article 220 standard method. Instant result with full line-by-line breakdown. Free, no account needed.
The Standard Method — NEC Article 220 Part III
The NEC Article 220 standard method calculates the minimum required service and feeder ampacity for a single-family dwelling. It works by summing loads in categories, applying demand factors where the NEC allows, then dividing by voltage to get amperes.
Most permit applications and AHJs accept this method. The optional method (NEC 220 Part IV) is an alternative for existing dwelling services — it often produces a smaller number, but requires knowing the actual measured demand.
The six steps
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1
General lighting load — NEC 220.12
3 VA per square foot of living area. Use outside dimensions, excluding unfinished spaces, open porches, carports, and garages. Include all finished habitable rooms regardless of actual fixture count.
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2
Small appliance and laundry circuits — NEC 220.52
Minimum two 20A small appliance circuits at 1,500 VA each = 3,000 VA. Plus one laundry circuit at 1,500 VA. These cannot be reduced by demand factors.
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3
Apply demand factors — NEC Table 220.42
Sum steps 1 + 2 and apply: first 3,000 VA at 100%, next 117,000 VA at 35%, remainder at 25%. This accounts for the fact that not all loads run simultaneously.
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4
Fixed appliances — NEC 220.53
Add the nameplate VA of all fixed appliances: dishwasher, garbage disposal, dryer (5,000 VA minimum or nameplate), water heater, range/oven. If four or more fixed appliances (excluding A/C, heating, dryer, and ranges), apply a 75% demand factor to that group.
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5
HVAC loads — NEC 220.60
Use the largest of heating or cooling (they don't typically run simultaneously). Add 100% of the largest motor plus 25% of all other HVAC motor loads per NEC 220.50. Electric heat uses the full nameplate VA.
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6
EV charger — NEC 625.41
EV charging is a continuous load — size at 125% of the EVSE ampacity. A 48A EVSE on a 240V/50A circuit = 48 × 1.25 × 240 = 14,400 VA. Add at full value — no demand factor reduction permitted.
NEC Article 220 residential load calculation is on every state licensing exam — typically 5–10 questions on a standard journeyman test. Know the 3 VA/sq ft rule, the Table 220.42 demand factor tiers (3,000/117,000 VA splits), and the 125% continuous load rule for HVAC and EV chargers. Use this calculator to check your hand-worked answers.
Worked Example — 2,400 sq ft Home
New construction, 2,400 sq ft finished area, natural gas heat, central A/C (5-ton, 7,200 VA), electric range (8,000 VA), dryer (5,000 VA), dishwasher (1,200 VA), water heater (4,500 VA), Level 2 EV charger (48A continuous).
Standard service sizes
After dividing total VA by 240V (single-phase), round up to the next standard service size:
| Calculated amps | Minimum service size | Typical use case |
|---|---|---|
| ≤ 100A | 100A | Small dwelling, gas heat, no EV charger |
| 101–150A | 150A | Mid-size home, gas heat and appliances |
| 151–200A | 200A | Most new homes — standard today |
| 201–320A | 320A | Large home, electric heat, EV charger |
| 321–400A | 400A | All-electric home, multiple HVAC, multiple EVSEs |
FAQ
What's the difference between the standard and optional method?
The standard method (NEC 220 Part III) uses VA/sq ft and demand factors from tables — it's conservative and works for any dwelling. The optional method (NEC 220 Part IV) uses actual measured loads and typically gives a smaller number, but requires the existing load data. For new construction and permit applications, use the standard method.
Do I include the garage square footage?
No. Exclude unfinished spaces, open porches, carports, and garages from the 3 VA/sq ft calculation. Include all finished habitable space — bedrooms, bathrooms, kitchen, living and dining rooms, finished basements.
How do I handle electric heat vs. A/C?
Per NEC 220.60, use the larger of the two loads — not both. If your electric heat is 15,000 VA and your central A/C is 7,200 VA, use 15,000 VA. They don't run simultaneously so the NEC allows this reduction.
My AHJ wants a load calc for a panel upgrade — do I need software?
No. This calculator produces the same numbers as any software. Print the page or copy the totals into your permit application. For complex commercial calculations, consider Kopperfield which specialises in permit-ready PDF load calc reports.
How does a Level 2 EV charger affect service size?
A 48A EVSE on a 240V/50A circuit adds 14,400 VA of continuous load (48 × 1.25 × 240). On a home that would otherwise need 130A of service, the EV charger alone pushes the requirement to 200A. This is one of the most common reasons for service upgrades in new residential construction.