Electrical Load Calculator
Service and feeder load for a single dwelling unit per NEC 220.82, the optional method used for most residential service sizing. Enter the floor area, dedicated-circuit appliances, and heating/AC; get the calculated load in amperes, the recommended standard service size, and every intermediate figure shown so the calculation can be checked line by line.
How to use this calculator
- Enter the floor area from outside dimensions, counting habitable space and areas adaptable to future use (unfinished basements count; open porches and garages don't, per NEC 220.5 and 220.82(B)(1)).
- Enter nameplate VA (or watts) for every appliance on a dedicated circuit: range, dryer, water heater, dishwasher, disposal, EVSE, well pump, and so on. Gas appliances count only their electrical load (igniters, blowers), typically small enough to fold into "other."
- Pick the heating/AC configuration (the 220.82(C) factor differs by system type) and enter the nameplate VA for each side.
- Read the calculated amps and the standard service size. The breakdown shows the 100%/40% demand split and the HVAC derivation for permit paperwork.
NEC reference
This calculator implements NEC 2020 220.82 (Optional Feeder and Service Load Calculation, single dwelling unit): general loads per 220.82(B), 3 VA/ft² lighting, 1500 VA per small-appliance and laundry circuit (minimums two and one per 210.11(C)), and appliance nameplates, with the first 10 kVA at 100% and the remainder at 40%; heating and air-conditioning per the largest applicable option in 220.82(C). The method applies to dwellings with a 120/240 V single-phase service of 100 A or greater. It is not the Part III standard method and does not cover multifamily (220.84) or existing-dwelling additions (220.83).
Results are for reference only. Verify against the applicable adopted edition of the NEC and consult a licensed electrician for code compliance.
Worked example: 2000 ft² all-electric dwelling
| Line | VA |
|---|---|
| General lighting: 2000 ft² × 3 VA | 6,000 |
| Two small-appliance circuits × 1500 VA | 3,000 |
| Laundry circuit | 1,500 |
| Range 12 kW + dryer 5.5 kW + water heater 4.5 kW + dishwasher 1.2 kW | 23,200 |
| General load subtotal | 33,700 |
| First 10 kVA @ 100% + 23,700 @ 40% | 19,480 |
| Heat 10 kW central @ 65% (larger than 5 kW AC @ 100%) | 6,500 |
| Total | 25,980 |
25,980 VA ÷ 240 V = 108.3 A → 110 A minimum standard rating, typically installed as a 125 A or 200 A service. These are the same numbers the calculator produces with its default inputs, so you can verify the tool against the worked example directly.
Frequently asked questions
Is a 200 amp service enough?
Usually. Most single-family homes calculate to 100-150 A under 220.82 even all-electric, so 200 A leaves headroom. The loads that change the picture are EV charging (48 A EVSE = 11.5 kVA at 100%), resistance heat in large homes, and pools or ADUs. Run your actual numbers above before paying for a service upgrade, and note NEC 625.42's energy-management allowance, which often makes an upgrade unnecessary for EV charging.
Standard method vs optional method: which should I use?
Either is code-compliant for a single dwelling on a 100 A+ service; the optional method is shorter and usually yields the same or a smaller service. Inspectors see 220.82 on most residential permits. The standard method matters when the dwelling doesn't qualify (service under 100 A) or when you need the category-by-category detail: range demand per Table 220.55, dryer per 220.54.
Why is heat taken at 65% but AC at 100%?
The 220.82(C) factors reflect diversity: central electric heat cycles and rarely runs every element simultaneously, so 65% is applied (40% with four or more separately controlled units, which stagger further). Compressors are taken at 100% because a running compressor draws its full load. Heat and AC never run together, so only the larger figure counts. That noncoincident-load rule is also why a heat pump's compressor and its supplemental heat are combined rather than compared.
What counts in the floor area?
Outside dimensions, including every floor of habitable space plus unfinished areas adaptable for future use (an unfinished basement or bonus room counts). Open porches, garages, and crawl spaces don't. When in doubt, include it; the 3 VA/ft² line is rarely what decides the service size, and counting more area errs conservative.
Seasonal guides
Adding up a temporary load rather than a dwelling service? The same watts-to-amps method sizes a holiday display and the generator that runs it.
- What Size Generator Do I Need for Halloween Decorations?: total the display in watts, leave headroom for surge, and put carbon-monoxide safety first.
Related calculators
- Breaker Size Calculator: size the individual branch circuits feeding these loads.
- Wire Size Calculator: service and feeder conductors for the calculated load.
- Wire Ampacity Calculator: verify conductor ampacity with derating.
- Voltage Drop Calculator: long service laterals and feeders to outbuildings.
Studying for the licensing exam? Our own NEC Code Quickstart works all twelve exam calculations start to finish, each with the code reference. Also in paperback.
Running an electrical contracting business? Jobber handles scheduling, invoicing, and job management. Start a 14-day free trial.
For deeper NEC training on load calculation and service sizing, Mike Holt's NEC courses are the industry standard.
Working from the printed code? NEC code books and tab sets are available from Mike Holt.
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