NEC Article 220 · dwelling service load
Electrical Load
Calculator
Size a home's electrical service the way the code does — add the loads, apply the NEC demand factors, and get the service you need. Because not everything runs at once, the calculated load lands well below the nameplate total. Standard & optional methods
For electricians sizing a service — and homeowners asking if they need 200 amps.
A 2,000 sq ft all-electric home calculates to about 124 A. Add an EV charger and it climbs to 174 A — a jump from a 125 A service to 200 A. Modern loads are why homes upgrade.
Both NEC methods
standard & optional (220.82)
Service size + headroom
100 to 200 A, with the verdict
NEC 2023, cited
every demand factor shown
Artie has taught physics and electrical theory for over a decade and consulted on real-world electrical design — so every tool here is grounded in both the theory and the field.
University physics lecturer·Consulted on commercial electrical systems·Last reviewed Jul 2026
Electrical Load Calculator
Size a one-family dwelling service — NEC-2023 standard & optional methods.
Enter the home details to size the service.
Calculated service load
Demand-factor stack — connected vs. calculated
Compare service sizes — tap to preview (loaded %)
How to use it
How to use the load calculator
Enter the home's floor area and its major electric loads, pick the standard or optional NEC method, and read the calculated demand — the service size it needs and the headroom left. Then decide: does the panel hold, or is it time to upgrade?
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01
Enter the home
Floor area, plus the big loads — range, dryer, water heater, HVAC, EV charger.
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02
Pick the method
Standard (each demand factor) or Optional 220.82 (the faster path).
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03
Read the load & service
The calculated demand, the service size it needs, and the headroom left.
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04
Apply it
Decide if the panel holds — then size the service wire and breaker.
The core idea
Connected load vs calculated load
Not everything runs at once — so the code sizes to a realistic peak.
A load calculation adds up a home's electrical demand to size its service. But the NEC doesn't use the raw nameplate total — because loads rarely run all at once, it applies demand factors that bring the connected load down to a realistic calculated load.
Same house, two numbers
Why the drop? The NEC applies demand factors:
- General lighting — 100% of the first 3 kVA, then 35%
- Four or more fixed appliances — 75%
- Heating vs A/C — the larger only, never both
Connected load — reduced by NEC demand factors — gives the calculated load, the number you size the service to.
The formula
The two NEC methods
Standard adds each demand factor; optional takes a shortcut. Same house — and the optional often lands smaller.
Same house, two answers — 150 A vs 125 A. The optional method (220.82) is faster and usually lands smaller; it's allowed for most dwellings. The standard method is more granular and is sometimes required — when in doubt, run both and confirm with your AHJ.
Standard: each category × its demand factor · Optional: 10 kVA @100% + 40% of the rest, plus HVAC
Worked example
Does this house fit its service?
A 2,000 sq ft all-electric home: 12 kW range, 5 kW dryer, water heater, dishwasher, disposal, microwave, and electric heat. Run the standard method, then check the answer against each service size.
The standard calculation
Does 144.6 A fit?
150 A is the minimum. The optional method puts the same house at 111 A → a 125 A service. Size up to 200 A for EV or heat-pump headroom.
Reference · NEC 2023
The demand factors, and the fine print
The reductions that turn a connected load into a calculated one — straight from NEC Article 220 — plus the honest limits of any online load calculator.
Key demand factors (NEC 2023)
| Load | Demand factor | NEC |
|---|---|---|
| General lighting | first 3 kVA @100%, rest @35% | 220.45 |
| Range (one, ≤12 kW) | 8 kVA (Column C) | 220.55 |
| Clothes dryer | 5 kVA or nameplate @100% | 220.54 |
| Fixed appliances (4+) | 75% | 220.53 |
| Heating vs A/C | larger only (noncoincident) | 220.60 |
| Optional method | 10 kVA @100% + 40% rest | 220.82 |
| EV charger | continuous, ×125% | 625.41 |
A screen, not a stamped study
This tool is for planning a one-family dwelling service. It's not a substitute for a permit-level load calculation. Codes are adopted locally — confirm the NEC edition in force, any local amendments, and your AHJ before service work.
Heads up — NEC 2026: Article 220 renumbers to Article 120; general lighting drops to 2 VA/sq ft and the optional first tier to 8 kVA. We build to NEC 2023 until your area adopts 2026.
Standard vs optional
Standard applies each category's demand factor; optional (220.82) uses 10 kVA @100% + 40% of the rest. Optional is faster and usually smaller — allowed for most dwellings.
Heat and A/C don't add
Heating and cooling never run together, so 220.60 counts only the larger of the two. Adding both is a common — and costly — over-sizing mistake.
Connected vs calculated
The nameplate total (connected) is always higher than the calculated load. You size the service to the calculated figure, not the sum of every label.
EV chargers are continuous
A Level 2 charger runs for hours, so 625.41 counts it at 125%. One EV charger often pushes a home from a 150 A to a 200 A service.
Dwellings only
These factors are for one-family dwelling units (house, condo, apartment). Commercial and multifamily house loads use different tables — this tool doesn't cover them.
What affects it
What drives the load — and what trips people up
A home's calculated load is mostly its big electric loads and its heat. The errors are rarely arithmetic — they're counting the wrong number, or double-counting loads the code says never run together.
What drives the load up
the big movers
- Electric heatElectric furnaces and heat pumps are the single biggest load in most all-electric homes.
- EV chargerA Level 2 charger counts at 125% — often the load that pushes a home to 200 A.
- Range & dryerThe two largest fixed appliances — big nameplate ratings, and demand tables of their own.
- Square footageFloor area sets the general lighting load at 3 VA per square foot — bigger home, bigger base.
Common mistakes
watch for these
- 01Connected, not calculatedAdding every nameplate and sizing to that total — the demand factors are the whole point.
- 02Counting heat + A/CThey never run together; 220.60 takes the larger only. Summing both over-sizes the service.
- 03Skipping demand factorsForgetting the 35% lighting and 75% appliance reductions inflates the result badly.
- 04Mixing NEC editions2023 and 2026 use different values — pick the edition your AHJ enforces and stay in it.
The point
Demand factors are why 190 A connected fits a 150 A service
The code assumes your range, dryer, heat, and EV charger won't all peak at the same second. That diversity — captured as demand factors — is what lets a realistic service carry a home whose labels add up to far more.
This is a planning screen, not a stamped study. Codes are adopted locally and amended — confirm the NEC edition in force, local amendments, and equipment nameplates with your AHJ and a licensed electrician before any service work.
Quick chart
What size service?
Enter a calculated load to see the service it needs and how loaded it is — or scan the table for what each standard service carries. A 145 A load needs a 150 A service.
The service is the next standard size at or above the calculated load.
Recommended service
150 A
145 A · 97% loaded
Standard service sizes (240 V)
| Service | Total | Cont. 80% | Typical home |
|---|---|---|---|
| 100 A | 24 kVA | 19.2 kVA | small / gas heat |
| 125 A | 30 kVA | 24 kVA | mid, some electric |
| 150 A | 36 kVA | 28.8 kVA | larger all-electric |
| 200 A | 48 kVA | 38.4 kVA | all-electric + EV |
Capacity = amps × 240 V. The 80% column is the continuous-load limit; size to the calculated load, not this ceiling.
| Service | 240 V total | 240 V @80% | 208 V total | 208 V @80% |
|---|---|---|---|---|
| 100 A | 24 kVA | 19.2 kVA | 20.8 kVA | 16.6 kVA |
| 125 A | 30 kVA | 24 kVA | 26 kVA | 20.8 kVA |
| 150 A | 36 kVA | 28.8 kVA | 31.2 kVA | 25 kVA |
| 200 A | 48 kVA | 38.4 kVA | 41.6 kVA | 33.3 kVA |
| 225 A | 54 kVA | 43.2 kVA | 46.8 kVA | 37.4 kVA |
| 400 A | 96 kVA | 76.8 kVA | 83.2 kVA | 66.6 kVA |
What is an electrical load calculation?
It's the method the NEC uses to size a home's electrical service — adding up the loads, applying demand factors, and converting to amps to find the minimum service size.
How do I calculate electrical load?
Total the general lighting (3 VA/sq ft), small-appliance, laundry, and appliance loads, apply the NEC demand factors, add the larger of heat or A/C, then divide by the service voltage (usually 240 V) to get amps.
What's the difference between the standard and optional methods?
The standard method applies a demand factor to each category. The optional method (220.82) takes 100% of the first 10 kVA plus 40% of the rest. Optional is faster and usually yields a smaller service.
What size electrical service do I need?
It depends on your calculated load. Most homes land on 100, 150, or 200 A; the service is the next standard size at or above the calculated amps. Run the calculator for your specific loads.
Do I need a 200 amp service?
If your calculated load exceeds about 150 A, yes. All-electric homes with electric heat, an EV charger, or a heat pump often cross that line — an EV charger alone can push a 150 A home to 200 A.
What is a demand factor?
A code-allowed reduction that reflects the fact that not everything runs at once. Demand factors turn the connected (nameplate) load into a realistic calculated load you size the service to.
What's the difference between connected and calculated load?
Connected is every nameplate added up. Calculated is that total after demand factors. You always size to the calculated figure — it's well below the connected sum.
Does an EV charger require a panel upgrade?
Not always, but it counts at 125% as a continuous load, so it can. Run a load calculation with the charger added — if the result exceeds your service, it's upgrade time.
Keep going
Related electrical calculators
Once you've got the service size, these size the rest of it: the service conductor, the main breaker, and the voltage drop on the run to the panel.
How we keep this accurate
This is a NEC-2023 dwelling (one-family) service-load screen, standard and optional methods. It's a planning estimate, not a stamped permit study — confirm the adopted NEC edition, local amendments, AHJ requirements, and equipment nameplates with a licensed electrician before any service work.