Service Entrance Load Calculator: NEC 220 Standard Method (Sq Ft + Appliances + HVAC)

How big should the electrical service be? It is the first question on every new build, every panel upgrade, every "can I add a hot tub / EV charger / heat pump" call. NEC Article 220 answers it with the standard method: a prescriptive, line-by-line load calculation that turns square footage and appliance nameplates into a single volt-ampere figure, and that figure into a service size. The calculator above runs the whole procedure — general lighting load, small-appliance and laundry circuits, the 220.42 demand factors, the 75% appliance rule, range and dryer demand, noncoincident HVAC, and EV charging. Enter your numbers, and it returns the calculated load in VA, the amperage at 240 V, and the minimum standard service rating.

Below the calculator: every step of the math with the code section that drives it, three worked examples you can check the calculator against, the standard service sizes, and the judgment calls that separate a passing load calc from a red-tagged one. If you are sizing a service upgrade, our service upgrade walkthrough covers the physical side, and panel bus bar ratings explains why the panel, not the meter base, is often the real constraint.

Step 1 — General Lighting and Receptacle Load (NEC 220.12 + 220.52)

The Code refuses to let you guess how much general load a house has. It prescribes it: 3 VA per square foot of living area (220.12, Table 220.12 dwelling units), measured from outside dimensions, excluding open porches and unfinished spaces not adaptable for future use. On top of that, 220.52 adds 1,500 VA per small-appliance branch circuit (minimum two, per 210.11(C)(1)) and 1,500 VA for the laundry circuit (210.11(C)(2)).

Load component	NEC section	Prescribed value	Example (2,000 sq ft)
General lighting & receptacles	220.12 / Table 220.12	3 VA per sq ft	6,000 VA
Small-appliance circuits	220.52(A)	1,500 VA each, 2 minimum	3,000 VA
Laundry circuit	220.52(B)	1,500 VA	1,500 VA
General subtotal	—	—	10,500 VA

Step 2 — The 220.42 Demand Factors

Nobody runs every light and every receptacle at once, and the Code knows it. NEC 220.42 applies demand factors to the general load: the first 3,000 VA counts at 100%, the portion from 3,001 to 120,000 VA counts at 35%, and anything beyond 120,000 VA at 25%. This is where the calc starts working in your favor — 10,500 VA of prescribed general load becomes 3,000 + 7,500 × 0.35 = 5,625 VA of calculated load.

Portion of general load	Demand factor	2,000 sq ft example
First 3,000 VA	100%	3,000 VA
3,001 – 120,000 VA	35%	7,500 VA → 2,625 VA
Over 120,000 VA	25%	rare in single-family

Step 3 — Fixed Appliances and the 75% Rule (NEC 220.53)

Fastened-in-place appliances — water heater, dishwasher, disposal, built-in microwave, trash compactor, instant-hot units — add at nameplate VA. The gift: when you have four or more, 220.53 lets you apply a 75% demand factor to the whole group. Three appliances: 100%. Four or more: 75%. Ranges, dryers, HVAC, and EV chargers are excluded from this group — they get their own treatment below.

Typical fixed appliance	Typical nameplate VA	Notes
Electric water heater (4.5 kW element)	4,500 VA	Both elements never fire simultaneously
Dishwasher	1,200 – 1,500 VA	Heated-dry cycle dominates
Garbage disposal	700 – 1,000 VA	Short duty, but counts
Built-in microwave	1,200 – 1,800 VA	Countertop units ride the small-appliance circuits
Instant water heater (point of use)	3,000 – 7,000 VA	Whole-house tankless is a different animal — see below
Trash compactor	800 – 1,200 VA	Motor load

Whole-house tankless water heaters deserve a warning: a 27 kW unit is 112.5 A at 240 V by itself. It is the single fastest way to turn a 200 A service into a 400 A conversation. If a customer insists on tankless electric, price the service upgrade, the larger panel, and the utility coordination before they fall in love with the spec sheet — the water heater is the cheap part of that job.

Service Conductors and Equipment Follow the Calc

The calculated amperage does not just pick the panel — it sets the service entrance conductors (230.42), the service disconnect rating (230.79), and the grounding electrode conductor size (Table 250.66). A 200 A service means 4/0 AWG aluminum or 2/0 AWG copper service conductors at 75°C, a 200 A disconnect, and a panel whose bus and main both carry the rating. Watch the used-beyond-nameplate trap: a "200 A" panel with a 200 A main breaker and a calculated load of 196 A is legal but has no room for the hot tub the customer will want next spring. When the calc lands within 10% of a rating, quote the next size up — panels are cheap, service upgrades are not.

Step 4 — Range and Dryer (NEC 220.55 / 220.54)

A household electric range up to 12 kW does not add 12,000 VA to the calc — Table 220.55 Column A assigns a single range a demand of 8,000 VA, because the elements cycle. Over 12 kW, Note 1 increases the 8 kW by 5% for each additional kW (a 14 kW range: 8,000 × 1.10 = 8,800 VA). The dryer (220.54) counts at nameplate or 5,000 W, whichever is larger — a 4.4 kW dryer still counts as 5,000.

Step 5 — HVAC: Noncoincident Loads (NEC 220.60)

Air conditioning and electric heat do not run at the same time, so 220.60 lets you count only the larger of the two. Use the unit's MCA-based VA or nameplate VA; for heat pumps with supplemental strip heat, the strips and compressor do coincide — add them. A 6,000 VA heat pump with 10 kW of strip heat is 16,000 VA of coincident load, not the larger of the two.

Step 6 — EV Charging (NEC 220.57)

Every dwelling-unit EV circuit adds 7,200 VA or the charger nameplate, whichever is larger. A 48 A charger on a 60 A circuit is 11,520 VA — nameplate wins. Planning a charger? Our Level 2 charger lineup covers the hardware side.

Step 7 — Total and Service Size

Sum everything, divide by 240 V, and round up to the next standard service rating. NEC 230.79(C) sets 100 A as the floor for a one-family dwelling with six or more 2-wire circuits — in practice, treat 100 A as the minimum, full stop.

Service size	Calculated load range	Typical application
100 A	≤ 100 A	Small home, gas appliances, no EV
125 A	100 – 125 A	Modest all-electric home without heat pump
150 A	125 – 150 A	Electric range + dryer + AC, no EV
200 A	150 – 200 A	The modern default: all-electric + one EV
225 A	200 – 225 A	200 A-class panels with 225 A bus
400 A	225 – 400 A	Large homes, two EVs, tankless WH, pools

Worked Examples

Example 1 — 1,500 sq ft starter home. General: 4,500 + 3,000 + 1,500 = 9,000 VA → demand: 3,000 + 6,000 × 0.35 = 5,100 VA. Range 8,000; dryer 5,000; water heater 4,500 + dishwasher 1,200 = 5,700 (two appliances, 100%); AC 4,000. Total 27,800 VA ÷ 240 V = 115.8 A → 125 A service.

Example 2 — 2,000 sq ft, typical all-electric. General 10,500 VA → 5,625 VA. Range 8,000; dryer 5,000; water heater 4,500 + dishwasher 1,200 + disposal 900 = 6,600 (three appliances, 100%); AC 5,000. Total 30,225 VA ÷ 240 V = 125.9 A → 150 A service — and this is exactly why 150 A panels exist.

Example 3 — 3,500 sq ft with electric heat and an EV. General 15,000 VA → 3,000 + 12,000 × 0.35 = 7,200 VA. Range 8,000; dryer 5,500 (nameplate over 5 kW); four appliances — 4,500 + 1,200 + 900 + 1,500 = 8,100 × 75% = 6,075; heat 12,000 beats AC 6,000; EV 7,200. Total 45,975 VA ÷ 240 V = 191.6 A → 200 A service, with almost no headroom. Add a second EV or a hot tub and you are in load-management (load management modules) or 400 A territory.

Standard Method vs. Optional Method

NEC 220.82–220.85 offer an optional method for dwellings served by a single 120/240 V or 208Y/120 V service: everything at 100% for the first 10 kW, 40% of the remainder, HVAC handled separately. It routinely lands one service size below the standard method — that same Example 2 house can pencil at 100–125 A. Two catches: your AHJ must accept it, and it assumes no future additions. Size for the house the customer will own in five years, not the one they closed on last month. When the panel is full but the calc passes, a generator interlock or transfer switch and smart load management can defer the service upgrade.

Getting the Material

Service equipment is a brand ecosystem decision — breaker type locks you in. We stock load centers, meter mains, and breakers from Square D, Siemens, and Eaton, with feeders and SER cable from Service Wire. Size the conductors with the NEC ampacity chart, protect them per the breaker sizing guide, and if you are still estimating consumption from utility bills, how to calculate power consumption will sharpen the inputs. For the code context behind every step, see the NEC compliance guide. Ready for a price? The calculator's quote button sends your calculated service size with the request, or browse panels and breakers directly.

Frequently Asked Questions

Is a 200 amp service enough for a house with an EV charger?

Usually, yes. A typical 2,000–3,000 sq ft all-electric home with one 48 A EV charger calculates to 150–190 A by the NEC 220 standard method. Two EVs, electric heat, or a tankless water heater can push past 200 A — run the calculator with your actual nameplates.

What is the difference between the standard and optional load calculation methods?

The standard method (220.12–220.61) applies prescriptive loads and demand factors line by line. The optional method (220.82–220.85) takes the first 10 kW at 100% and the remainder at 40% plus HVAC, and typically yields a smaller service. Both are legitimate; the AHJ has final say.

Does the 75% appliance demand factor apply to three appliances?

No. NEC 220.53 requires four or more fastened-in-place appliances before the 75% demand factor applies. With three or fewer, each counts at 100% of nameplate. Ranges, dryers, HVAC, and EVSE never join this group.

Why does a 12 kW range only add 8 kW to the load calc?

Table 220.55 reflects diversity: range elements cycle on and off, so a single household range up to 12 kW carries a demand of 8,000 VA. Over 12 kW, add 5% per additional kW per Table Note 1.

Do I count heating and cooling together?

No — NEC 220.60 treats them as noncoincident: count only the larger. Exception: heat pumps with supplemental strip heat can run both simultaneously, so add compressor and strips together.

How many VA does an EV charger add to a residential load calc?

NEC 220.57 requires 7,200 VA or the charger nameplate, whichever is larger, per dwelling-unit charger. A 48 A unit at 240 V is 11,520 VA — nearly 48 A of the service by itself.