How to Calculate a Residential Electrical Load (NEC Article 220)
A dwelling load calculation determines the size of the electrical service and main panel a home needs. Undersize it and breakers nuisance-trip or conductors overheat; oversize it and you pay for capacity you'll never use. NEC Article 220 gives two accepted routes — the Standard method and the Optional method — and this tool runs both so you can compare.
Standard Method (Article 220, Part III)
The Standard method totals each category with its own demand factor:
→ Table 220.42: first 3000 VA @ 100%, 3001–120,000 @ 35%, rest @ 25%
+ Range demand (Table 220.55: ≤12 kW → 8000 VA)
+ Dryer demand (220.54: max of nameplate or 5000 VA)
+ Fixed appliances (220.53: ×0.75 if four or more)
+ Larger of A/C or heating (220.60)
Service current = Total VA ÷ 240
Optional Method (220.82)
Permitted for any dwelling served at 100 A or more, this method is simpler and usually gives a smaller result. All general and appliance loads (at nameplate, excluding heating and cooling) are summed; the first 10 kVA is taken at 100% and everything above at 40%. A percentage of the heating or cooling load is then added — 100% for a heat pump or A/C, 65% for central electric heat, or 40% where there are four or more separately controlled units — using whichever is largest.
Standard Service Sizes
| Service (A) | Typical dwelling |
|---|---|
| 100 | Small home, gas heat/range, no A/C |
| 125 | Modest home with central A/C |
| 150 | Mid-size home, electric range + A/C |
| 200 | Most modern homes (common default) |
| 300–400 | Large or all-electric homes, EV + pool |
Key Demand Factors Explained
General lighting (220.42): not every outlet is used at once, so beyond the first 3000 VA only 35% is counted.
Range (220.55): a single range up to 12 kW counts as 8 kW because burners rarely run together at full power.
Dryer (220.54): counted at nameplate or a 5000 VA minimum, whichever is larger, for a single unit.
Fixed appliances (220.53): four or more fastened-in-place appliances may be taken at 75%, reflecting diversity.
Noncoincident loads (220.60): heating and cooling never run together, so only the larger is included.
Worked Example
A 2,000 ft² home with a 10 kW range, 5 kVA dryer, 6 kVA of fixed appliances (5 units), 5 kVA A/C, no electric heat, Standard method:
- General = 2000×3 + 3×1500 = 10,500 VA → 3000 + (7500×0.35) = 5,625 VA
- Range = 8,000 VA · Dryer = 5,000 VA · Fixed = 6,000 × 0.75 = 4,500 VA · A/C = 5,000 VA
- Total = 5,625 + 8,000 + 5,000 + 4,500 + 5,000 = 28,125 VA
- Current = 28,125 ÷ 240 ≈ 117 A → 125 A service
Enter these figures above to confirm and to compare with the Optional method.
Common Mistakes
- Counting a range or dryer at full nameplate instead of its demand value.
- Adding A/C and heating together rather than taking the larger.
- Forgetting the 75% factor when four or more fixed appliances are present.
- Capping the service at 200 A when a large all-electric home needs 300–400 A.
- Omitting newer loads such as EV chargers, which must be added per Article 625.