Enter your home's square footage and appliance nameplates, and get the calculated service load in amps from both NEC Article 220 methods — Standard and Optional — with every demand factor built in and the EV charger counted at 125%.
What Your Results Mean
Two takeoffs run in parallel because the code offers two legal answers. The Standard Method builds the estimate piece by piece — lighting demand, range demand, dryer floor, the 75% factor, the larger of heat or cool — and it is the method most plans examiners learned first. The Optional Method pools every general load at nameplate, applies a single demand factor of 100% on the first 10,000 VA and 40% on the rest, then adds heat or cooling at full value. Same house, same code edition: the Optional typically lands 15–25% lower, because it trusts the statistics of big loads never coinciding.
The inputs are nameplates, and nameplates live on the appliance: a water heater's rating is on its label plate, a dryer's is inside the door or on the back, an AC compressor's is on the outdoor unit (look for RLA — rated load amps — and multiply by 230, or use the MCA already printed beside it). Gas appliances enter as zero everywhere, which is exactly why gas homes calculate so much smaller: the range, dryer, water heater, and furnace all vanish from the arithmetic at once. If an appliance is plug-in rather than fastened in place, it still counts — the code treats cooking and laundry equipment as fixed loads regardless of the cord.
The suggested service size rounds the larger of your two method results up to the next common size — 100, 125, 150, 200, or 320 amps. Permits accept either method, but margin only ever comes from the bigger number. Two upgrades cost double what one does; nobody has ever regretted the size that cleared the calculation with room for the heat pump they bought three years later. A load calc is also a snapshot: anything you are actively planning — the charger, the hot tub, the workshop welder — belongs in the inputs now, not after the panel is installed.
Reading the Lines
- Lighting + small circuits: 3 VA per square foot of finished area, plus the two kitchen small-appliance circuits and the laundry circuit the code requires in every dwelling. The demand factor then discounts everything past the first 3,000 VA to 35% — eighty years of measured behavior, not a loophole.
- Range: the demand table, not the nameplate. A single range up to 12 kW counts as 8,000 VA; larger ranges add 5% per kW above 12. The oven and every burner on high for an hour is a Thanksgiving scenario the code has already priced in.
- Fixed appliances: water heater, dishwasher, disposal, and anything else fastened in place. Four or more of them triggers the 75% factor — the disposal and the dishwasher genuinely never run together.
- Heat or cool: the larger of the two, never both — the furnace and the compressor cannot peak simultaneously. The motor add-on on top (25% of the largest motor, usually the compressor) covers the extra current motors draw while starting.
- EV charger: a continuous load, so the code counts it at 125% of its rating. A 48-amp charger contributes 14,400 VA — 60 amps of the calculation all by itself.
What the Calculator Does Not Do
It sizes the service, not the circuits inside it — branch-circuit and feeder sizing (wire size, conduit fill, breaker coordination) is a separate chapter of the code and a separate visit from the electrician. It does not model energy-management schemes: an EVSE that sheds the dryer while charging, or a load-management system approved by your utility, can fit a charger onto a service the plain arithmetic says is full. It also cannot see your local amendments — jurisdictions adopt different code editions and add their own rules, and the adopted local code always wins. For a binding number on a permit, a licensed electrician runs this same arithmetic with the panel open in front of them.
Pro Tip
Ask which method your plans office prefers before you size an upgrade. The Standard Method's answer runs higher, and on a house sitting near a size boundary — 135 amps, say — the choice between 137 and 109 is the choice between a 150-amp and a 125-amp service. The Article 220 guide walks both methods by hand.
The Math Behind the Calculator
Both methods start the same way — your house as a list of volt-amps — and then diverge in how they discount it:
lighting = area × 3 VA + 2 × 1,500 + 1,500
heat_or_cool = max(electric_heat, compressor + blower)
ev = charger_amps × 240 × 1.25
standard = lighting_demand + range_demand + dryer + fixed + ev + heat_or_cool + 0.25 × largest_motor
optional = 10,000 + 0.40 × (general_loads − 10,000) + heat_or_cool + ev
amps = total VA ÷ 240
Every demand factor in those lines is the code pricing in human behavior. The two tables below are the ones the Standard Method leans on:
The Optional Method replaces all of that with one line: 100% of the first 10 kVA of pooled general loads, 40% of everything above it, then heating or cooling at nameplate with no motor add-on. The range counts at its full nameplate rather than the 8,000 VA demand value, which is why the Optional Method's general-load pool looks larger before its demand factor — and smaller after it. Dividing by 240 volts turns volt-amps into service amps, because a residential service is a 120/240-volt split-phase system: 240 across both legs, and the calculation rides both.
Assumptions & Limitations
Every number above rests on these constants. If your house differs, change the matching input — or read the linked guide for the full reasoning.
- Single-family dwelling, 120/240 V split-phase service (the Optional Method additionally assumes a 100 A+ service)
- Area is finished living space — outside dimensions, open porches and garages excluded
- VA treated as equivalent to watts, standard for residential calculations
- The EV charger is counted at 125% as its own line in both methods — the conservative treatment; some jurisdictions allow it inside the Optional Method's 40% pool
- Largest motor assumed to be the AC compressor (or heat pump) when cooling is present
- Gas appliances count as zero — enter 0 for a gas range, dryer, water heater, or furnace
- Heat pumps: enter the compressor and blower under cooling; resistance backup strips go under electric heat
- Local amendments and the adopted code edition always win — verify with your electrician and AHJ before a permit
Worked Example: 2,400 Square Feet, Gas Heat
The same house walked through in the Article 220 service load guide, so every number below is checkable against it. Leave the defaults as they load: 2,400 sq ft, 12 kW range, 5,000 VA dryer, 4,500 VA water heater, dishwasher, disposal, gas heat, and central air at 5,280 VA compressor + 660 VA blower:
- Lighting subtotal: 7,200 + 3,000 + 1,500 = 11,700 VA → demand brings it to 6,045 VA.
- Range: 12 kW → 8,000 VA. Dryer: 5,000 VA.
- Three fixed appliances (water heater, dishwasher, disposal) — no 75% factor yet: 6,600 VA.
- Cooling, the larger of heat or cool: 5,280 + 660 = 5,940 VA, plus 25% of the compressor, 1,320 VA.
- Standard total: 32,905 VA ÷ 240 = 137 A — a 150-amp service to clear it with margin.
- Optional Method: 35,300 VA of general loads → 10,000 + 40% × 25,300 = 20,120, plus 5,940 cooling = 26,060 VA ÷ 240 = 109 A.
Now add the charger — type 48 into the EV field and watch what one purchase does. The Standard Method climbs by 14,400 VA to 47,305 — 197 amps, a 200-amp service, full stop. The Optional Method lands at 168 amps. That is the honest arithmetic behind "the EV charger tipped the house to 200 amps": same house, same panel, one continuous load. It is also why utilities and inspectors now ask about charging plans before approving panel upgrades, and why load-management chargers that shed other loads mid-charge have become the alternative to digging up the yard.
Run your own house both ways before you believe either number. If your two methods disagree by more than about 30%, an input is usually wrong — most often a gas appliance entered as electric, or a compressor nameplate read as amps instead of VA. And when the calculator says 150, remember what the number buys: not just the panel, but the conductors from the street, the meter base, and the main. Sizing the service is a utility coordination job, not a box swap.