How it works
Optional (220.82): 100% of first 10,000 VA + 40% of the remaining general load, plus the larger HVAC load demand-factored by type under 220.82(C) (A/C and heat pump 100%, central or <4-unit electric heat 65%, 4+ heaters 40%), plus EVSE at 100%. Standard (Part III): general lighting under Table 220.42 + range (Table 220.55 Col. C) + dryer (220.54) + fixed appliances (220.53) + larger of heat/cool (220.60) + EVSE (220.57), all at 100%. Service amps = total VA ÷ service voltage; round up to the next standard size (240.6), never below 100 A (230.79(C)).
The compact readout shows the recommended service size as the headline, then four decision metrics: total calculated VA, the demand-factored general load, the HVAC load that survived 220.60, and the optional-vs-standard comparison. The full per-category worksheet — each line at its own NEC article — expands as follows. The general load is the sum of 3 VA per square foot of living area (NEC 220.12), two or more small-appliance circuits and the laundry circuit at 1,500 VA each (220.52), and the nameplate of the fixed appliances. The optional method (220.82) lumps the range and dryer into that general load and applies a generous 100%/40% demand factor — 100% of the first 10,000 VA plus 40% of the remainder — which is why it usually lands lower than the standard method. The standard method instead itemises each category: it applies Table 220.42 to lighting (100% of the first 3,000 VA, 35% of the rest), looks the range up in Table 220.55 Column C (8,000 VA for a single range up to 12 kW), takes the dryer at 5,000 VA or nameplate (220.54), and discounts four or more fastened-in-place appliances to 75% (220.53). Both methods take only the larger of heating or cooling under 220.60 — the most common student error is adding both. The optional method then demand-factors that HVAC load by type under 220.82(C): air conditioning and heat pumps without supplemental heat at 100%, central electric space heating or fewer than four separately-controlled electric heaters at 65%, and four or more separately-controlled heaters at 40% — pick the heating type that matches your install so a heat-dominant home is not over-sized. The EV charger is the second-most-common error: under 220.57 and 220.82(B)(4) it is added on its own line at 100% of nameplate (a 7,200 VA minimum for any EVSE, with no Level-1 exemption) after the demand factor, never inside the 40% tier, and is rolled into the total VA you see. The recommended size is that total VA divided by the service voltage, rounded up to the next standard ampere rating (240.6). Finally, NEC 230.79(C) sets a 100 A floor for a one-family dwelling, so even an 80 A calculated load still needs a 100 A service; the headline flags "code minimum applies" when the calculation lands below 100 A. Check the conductors feeding the service against the voltage drop on the run once you pick a size.
Code references
- General lighting unit load (3 VA/ft²) NEC 2023, 220.12 and Table 220.12
- Small-appliance and laundry branch circuits (1,500 VA each) NEC 2023, 220.52(A) and 220.52(B)
- Lighting demand factors (100% first 3 kVA, 35% remainder) NEC 2023, Table 220.42
- Fastened-in-place appliances (75% for 4 or more) NEC 2023, 220.53
- Household clothes dryer (5,000 VA minimum) NEC 2023, 220.54 and Table 220.54
- Household cooking equipment (Column C, single range) NEC 2023, 220.55 and Table 220.55
- Noncoincident loads — larger of heating or cooling only NEC 2023, 220.60
- Optional method for dwelling units (100%/40% general load) NEC 2023, 220.82 and 220.82(B)
- Optional-method HVAC factors (A/C 100%, central/<4 heat 65%, 4+ heat 40%) NEC 2023, 220.82(C)
- EV charging system load (100% nameplate, 7,200 VA minimum) NEC 2023, 220.57 and 220.82(B)(4)
- Minimum service size for a one-family dwelling (100 A) NEC 2023, 230.79(C)
- Standard ampere ratings (next service size) NEC 2023, 240.6(A)
FAQ
Can I include my EV charger in the 40% general-load tier?
No. Under NEC 220.82(B)(4) and 220.57, an EV charging system (EVSE) is added at 100% of its nameplate rating — a 7,200 VA minimum for ANY EV charger (the code sets no Level-1 exemption, so even a 1,440 VA Level 1 cord counts as 7,200 VA) — after the 100%/40% general-load demand factor, never inside it. Folding it into the 40% tier under-counts the load and is the single most common mistake in online calculators. This tool always adds it on its own line at 100%.
My calculation came out at 87 A — why do I still need a 100 A service?
NEC 230.79(C) sets a minimum service and feeder rating of 100 A for a one-family dwelling, regardless of the calculated load. So an 87 A calculated load still requires a 100 A service. The tool flags this with the note "code minimum applies" whenever the calculated demand lands below 100 A.
Which method does my inspector want — optional or standard?
Most authorities having jurisdiction (AHJs) accept the optional method (NEC 220.82) for a single-family dwelling, and it usually produces a lower, permit-acceptable number. For a small or heat-dominant home, though, the optional method can come out higher — this tool shows both side by side and the comparison metric tells you which is lower, so you can submit whichever your AHJ asks for. Some inspectors require the standard Part III calculation; confirm with your local inspector before you pull the permit.
Do I count both my heating and my air conditioning?
No. NEC 220.60 treats heating and cooling as noncoincident loads because they never run at the same time, so you include only the larger of the two. If you enter both, the calculator automatically uses the larger and notes which one it excluded — a 15,000 VA electric furnace would override an 11,200 VA A/C, for example.
Why does the optional method give a lower number?
The optional method (220.82) applies a single generous demand factor — 100% of the first 10,000 VA of general load and only 40% of everything above it — and rolls the range and dryer into that general load. The standard method instead applies smaller, category-by-category demand factors (Table 220.42 for lighting, Table 220.55 for the range, and so on) that add up to more. For a typical home the optional method lands 10–20 A lower, which is why it is the field default. It is not guaranteed lower, though: a small home has little load above the 10,000 VA break to discount, and a heat-dominant home only gets the 65%/40% heating factor of 220.82(C), so for those the standard method can win — always check the comparison metric.
How is the range demand of 8,000 VA derived?
NEC Table 220.55, Column C gives the demand for household cooking equipment. For a single range with a nameplate of 12 kW or less, the demand is a flat 8,000 VA — so an 8.75 kW range and a 12 kW range both count as 8,000 VA. Above 12 kW, Column C increases 5% for each kilowatt — or major fraction thereof — over 12 (Note 1); this tool rounds to the nearest kilowatt, so a 12.4 kW range still counts as 8,000 VA while a 12.5 kW range bumps to 8,400 VA.
This calculator is provided for estimation purposes only. A residential service load calculation should be reviewed and sealed where required by a licensed electrician or electrical engineer, and verified against the current NEC edition and your local amendments and AHJ requirements before sizing a service or pulling a permit.