Electrical load & service size calculator
This calculator sizes the electrical service for a single-family, single-phase 120/240 V dwelling to the 2023 National Electrical Code. Enter the floor area, the branch-circuit counts, every fixed appliance, the heating and cooling equipment and an EV charger, and it returns the calculated demand in volt-amperes, the demand current in amps and the smallest standard service that carries it — all computed in your browser, with nothing uploaded.
Reach for it in three situations. When you are sizing a service for a new build, it totals the whole dwelling and recommends a minimum rating. When you already have a 100 A or 200 A panel and want to know whether it will take a heat pump or an EV charger, it shows the headroom left on the existing service. And when you need a permit worksheet, it lists every load with the NEC article that governs it, ready to print or export.
The tool offers the three methods the code actually uses. The Optional method (220.82) is the fastest and the usual choice for a whole modern all-electric dwelling. The Standard method (220.40–.55) applies each load's own demand factor line by line and is what many inspectors expect on a formal worksheet. The Existing-dwelling method (220.83) is the one to use when you are adding a load to a panel that already serves a home — it is the most generous of the three for that case. Switch between them over the same load inventory and watch the number change.
Every NEC demand factor and every default nameplate value is exposed as an editable field, because none of them should be hidden inside the math. The defaults are typical 2023-edition figures — verify each against a current copy of the code and your equipment nameplates before you rely on the result. This is an estimate, not a substitute for a licensed electrician or your authority having jurisdiction.
The three NEC calculation methods
The Optional method — NEC 220.82 — pools the general lighting load (3 VA/ft²), the two small-appliance circuits and the laundry circuit (1500 VA each) together with the nameplate rating of every appliance except heating and cooling. It takes the first 10 kVA of that pool at 100% and everything above it at 40%. Ranges, ovens and dryers go in at full nameplate here — the Table 220.55 range factors do not apply. Heating and cooling are then added by 220.82(C), which takes only the single largest of the air-conditioning, heat-pump and electric-space-heat clauses, never the sum.
The Standard method — NEC 220.40 through 220.55 — does not pool the loads. It applies each load's own demand factor: general lighting through the Table 220.42 tiers (first 3000 VA at 100%, the next band at 35%, the remainder at 25%); fastened-in-place appliances at 75% once there are four or more of them (220.53); the electric range through Table 220.55 (220.55(C)); the dryer at the greater of 5000 VA or nameplate (220.54); and heating versus cooling as noncoincident loads, counting only the larger (220.60). It is more granular and often the figure a formal permit expects.
The Existing-dwelling method — NEC 220.83 — is for adding load to a home that is already wired. It reuses the pooled-bucket shape of the Optional method but takes the first 8 kVA at 100% (rather than 10 kVA) and the remainder at 40%, which produces a lower, code-legitimate number for the same inventory. When you are adding new air-conditioning or electric heat, 220.83(B) pulls that new equipment out of the bucket and counts it at 100% instead; otherwise the existing heating and cooling ride inside the bucket with everything else. This is the method behind the flagship "will my panel take an EV charger?" question.
The EV charger is handled the same way in every method. NEC 220.57 takes the larger of 7200 VA or the EVSE nameplate, at 100%, added as its own line outside the general pool — the conservative reading of the 2023 code. If the installation uses an automatic energy-management system (EVEMS, 625.42), the contribution can be capped at the managed value, which is often what brings an EV charger onto an existing panel without a service upgrade.
Demand-factor reference
The table below sets the Optional and Standard methods side by side so you can see why the same house can produce two different demand figures. The Optional method's strength is the single 10 kVA / 40% bucket; the Standard method's is the per-load factors, especially the range and the four-appliance rule. Every value shown is an editable default in the tool — the numbers here are the 2023-edition figures the engine ships with.
How each load is treated under the two whole-dwelling methods. Values are the editable engine defaults.
| Load | Optional (220.82) | Standard (220.40–.55) |
|---|---|---|
| General lighting (220.12) | 3 VA/ft², in the 10 kVA / 40% pool | 3 VA/ft², Table 220.42 tiers |
| Small-appliance circuits (220.52) | 1500 VA each, in the pool | 1500 VA each, in the 220.42 pool |
| Laundry circuit (220.52) | 1500 VA, in the pool | 1500 VA, in the 220.42 pool |
| General-load demand factor | First 10 kVA at 100%, remainder at 40% | Per-load factors (no single pool) |
| Range / oven (220.55) | 100% of nameplate | Table 220.55(C): 8 kW for a single ≤12 kW range |
| Clothes dryer (220.54) | 100% of nameplate | Greater of 5000 VA or nameplate |
| Fixed appliances (220.53) | 100% of nameplate, in the pool | 75% once four or more |
| Heating & cooling | 220.82(C): largest single clause | 220.60: larger of heat vs A/C at 100% |
| EV charger (220.57) | Max(7200 VA, nameplate) at 100%, outside the pool | Max(7200 VA, nameplate) at 100%, own line |
Ranges and EV chargers
Household electric ranges are the one load where the two methods diverge sharply. Under the Optional and Existing methods the range enters the pool at 100% of its nameplate. Under the Standard method it is governed by Table 220.55: a single range rated 12 kW or less has a fixed demand of 8 kW, and a single range above 12 kW adds 5% for each kilowatt (or major fraction) over 12. The excerpt below shows that Column C rule for common nameplate sizes.
EV chargers are the load that most often decides whether an existing service survives a new addition. NEC 220.57 counts the EVSE at the larger of 7200 VA or its nameplate, at 100%, on its own line outside the general demand pool. A 48 A charger is 11,520 VA; a 40 A charger is 9600 VA; a 32 A charger is 7680 VA. Where an automatic load-management system (EVEMS) is installed, NEC 625.42 lets you substitute the managed maximum for the raw nameplate — the code-sanctioned way to add a charger to a panel that is otherwise full.
Standard-method demand for one range by nameplate rating: 8 kW for 12 kW or less, plus 5% per kW above 12 kW.
| Nameplate | Column C demand |
|---|---|
| 8 kW | 8.0 kW |
| 10 kW | 8.0 kW |
| 12 kW | 8.0 kW |
| 14 kW | 8.8 kW |
| 16 kW | 9.6 kW |
| 18 kW | 10.4 kW |
| 20 kW | 11.2 kW |
Worked example
This is an all-electric 2000 ft² dwelling sized by the Optional method against a 200 A service, drawn with the very gauge and breakdown bar the tool renders live. It shows how the general pool, the largest HVAC clause and the EV line combine into the demand current and the recommended minimum service.
- Given
- 2000 ft² floor area · 2 small-appliance circuits · 1 laundry circuit
- Range 8000 VA · dryer 5000 VA · water heater 4500 VA · dishwasher 1500 VA
- Central A/C 5760 VA (2.5 ton) · EV charger 11,520 VA (48 A)
- Optional method (220.82) · 200 A service at 240 V
- Calculation
- General pool = 6000 (lighting) + 3000 (small-appliance) + 1500 (laundry) + 8000 + 5000 + 4500 + 1500 = 29,500 VA
- Pool demand = 10,000 (first 10 kVA at 100%) + 40% × 19,500 = 17,800 VA
- HVAC 220.82(C): A/C at 100% is the largest clause = 5760 VA
- EV 220.57: max(7200, 11,520) at 100%, outside the pool = 11,520 VA
- Total demand = 17,800 + 5760 + 11,520 = 35,080 VA → 35,080 ÷ 240 ≈ 146 A
- Result
- ≈146 A of 200 A — passes with about 54 A of headroom; recommended minimum service 150 A.
Load breakdown
- General lighting3,620 VA
- Small appliance1,810 VA
- Laundry905 VA
- Fixed appliances3,620 VA
- Range4,827 VA
- Dryer3,017 VA
- HVAC5,760 VA
- EV charger11,521 VA
Optional-method demand for the all-electric example against a 200 A service, with the standard service rungs as tick context.
How to size a service with this calculator
- Choose method and unitsPick the Optional, Standard or Existing-dwelling method and set imperial or metric — only the floor area changes with the unit system; every electrical value stays in VA and amps.
- Add the loadsEnter the floor area and the small-appliance and laundry circuit counts, then add each appliance. Picking a category prefills a typical nameplate you can override.
- Enter HVAC and EVAdd the air-conditioning, heat-pump or electric-space-heat nameplates and any EV charger. Toggle EVEMS to cap a managed charger under NEC 625.42.
- Read the service sizeRead the demand amps, the pass/fail verdict and the recommended minimum service on the gauge, then export the CSV or print the article-cited worksheet.
Frequently asked questions
Which method should I use?
For a whole new all-electric dwelling the Optional method (220.82) is the usual fastest choice. When a formal permit worksheet is expected, the Standard method (220.40–.55) applies each load's own factor line by line. When you are adding a load to a home that is already wired — the classic EV-charger or heat-pump upgrade — the Existing-dwelling method (220.83) gives the most favorable code-correct number. The tool runs the same inventory through all three so you can compare.
What size service do I need?
Divide the calculated demand in volt-amperes by the service voltage (240 V by default) to get demand amps, then pick the smallest standard rating that is at least that large. The common residential rungs are 100, 125, 150, 200 and 400 A. The calculator highlights the recommended minimum rung on the gauge and flags when your selected service is exceeded.
Will my existing panel take an EV charger or heat pump?
Enter your whole-house loads plus the new charger or heat pump and read the headroom on the gauge. If the demand exceeds the service, the Existing-dwelling method (220.83) often produces a lower number, and an automatic load-management system (EVEMS, NEC 625.42) can cap the EV contribution — both are code-legitimate ways to fit a new load without upsizing the service.
Does this size the wires or conductors?
No. This sizes the service by demand load only; it does not size conductors or apply the NEC 310.12 83% dwelling-service allowance. Use a wire-size or voltage-drop calculator for the conductors once you have the demand current.
Can I use this for a permit?
Treat it as an estimate and a starting worksheet, not an official document. Every demand factor is an editable default triangulated from secondary sources, not primary-verified, and the NEC edition your jurisdiction adopts may differ. Always confirm the factors and the final service size against a current copy of the code and your authority having jurisdiction.