Calculate a home’s total electrical load in VA and amps and find the service size you need, using the NEC standard or optional method.
Electricity Load Formula
Two calculation paths are recognized for a single dwelling. The standard method applies a separate demand factor to each category of load. The optional method pools most loads into one bucket and applies a two step demand factor to the total.
Standard method (NEC 220.40 through 220.55, renumbered as Article 120 in the 2026 NEC):
Optional method (NEC 220.82, renumbered 120.82 in the 2026 NEC):
Both methods finish the same way:
- GL = connected general lighting and receptacle load, in VA
- A = habitable floor area, in square feet, measured to the outside of the walls
- U = unit load, 3 VA per square foot in the 2017 through 2023 NEC and 2 VA per square foot in the 2026 NEC
- Nsa = number of small appliance branch circuits, minimum 2
- Nl = number of laundry branch circuits, minimum 1
- GD = general load after the dwelling demand factors, first 3000 VA at 100 percent and the remainder at 35 percent
- RD = cooking equipment demand from Table 220.55, which is 8000 VA for one range rated 12 kW or less
- DD = dryer demand, the nameplate rating or 5000 VA, whichever is larger
- FD = fastened in place appliance demand, taken at 100 percent for three or fewer qualifying units and 75 percent for four or more
- HD = heating or cooling demand, the larger of the two when they cannot run at the same time
- EV = electric vehicle supply equipment load, the nameplate rating or 7200 VA, whichever is larger
- OL = other loads such as a pool, spa, well pump or workshop subpanel
- B = optional method load bucket, the sum of the general load and every appliance nameplate except heating and cooling
- SUMnameplate = sum of nameplate ratings for the range, dryer, water heater and other fastened in place appliances, in VA
- T = first tier taken at 100 percent, 10,000 VA in the 2017 through 2023 NEC and 8000 VA in the 2026 NEC
- I = calculated service current, in amps
- V = service voltage, 240 V for a 120/240 V service and 208 V for a 208Y/120 V service
The solve for selector switches between sizing a new service and testing how much room is left on a service that already exists. The method selector runs the standard path, the optional path, or both at once so you can see which one produces the lower number. The NEC edition selector changes U and T, which are the two values that moved in the 2026 code. The HVAC selector controls how HD is built: a single system is taken at 100 percent, a system that has both heating and cooling keeps only the larger load because they are noncoincident, and a heat pump with strip heat adds the compressor and the strip heat together because both can energize at once. The appliance count field decides whether FD gets the 75 percent factor. Rounding the result up to the next standard service rating gives the 100, 125, 150, 175, 200, 225, 300 or 400 amp answer.
Code Edition Changes and Service Headroom
The 2026 NEC moved load calculations out of Article 220 and into Article 120, and it changed two numbers that every residential load calculation depends on. Running the same house under both editions is the fastest way to see the size of the shift.
| Rule | 2017 to 2023 NEC | 2026 NEC | Effect on a 2,000 sq ft home |
|---|---|---|---|
| Article number | Article 220 | Article 120 | Section references change, math is unaffected |
| Unit load for service calculations | 3 VA per sq ft | 2 VA per sq ft | General load drops from 6000 VA to 4000 VA, and after demand factors the general demand falls from 5625 VA to 4925 VA |
| Unit load for branch circuit counting | 3 VA per sq ft | 3 VA per sq ft | The minimum number of lighting circuits does not drop |
| Optional method first tier | 10,000 VA at 100 percent | 8000 VA at 100 percent | A 34,400 VA bucket falls from 19,760 VA to 18,560 VA of demand |
| EV charging under the optional method | Treated as an additional load inside the bucket | 100 percent of nameplate, added outside the bucket | An 11,520 VA charger adds about 4600 VA under the older reading and the full 11,520 VA under 2026 |
| Multiple dryer demand reduction | Starts at the fifth dryer | Starts at the third dryer | No effect on a single family home |
| 125 percent factor for continuous loads | Applied in the load calculation | Removed from the load calculation | Still applies when sizing conductors and breakers |
Check which edition your jurisdiction has adopted before you use a result. Adoption lags publication by years in most states, so a 2026 answer can be rejected by an inspector still working from the 2020 code.
Sizing a service is only half the question. The other half is how much of that service is left over, which is what decides whether an EV charger or a heat pump can be added without an upgrade. A continuous load such as EV charging is sized at 125 percent of its rating, so the spare amps below are divided by 1.25 to get the largest charger that fits.
| Calculated load | Smallest service | Spare on a 100 A service | Spare on a 200 A service | Largest EV charger on 200 A |
|---|---|---|---|---|
| 60 A (14,400 VA) | 100 A | 40 A | 140 A | 80 A or more, panel space is the limit |
| 90 A (21,600 VA) | 100 A | 10 A | 110 A | 80 A or more |
| 127 A (30,525 VA) | 150 A | over by 27 A | 73 A | 58 A |
| 160 A (38,400 VA) | 175 A | over by 60 A | 40 A | 32 A |
| 185 A (44,400 VA) | 200 A | over by 85 A | 15 A | 12 A, so load management hardware is needed |
| 210 A (50,400 VA) | 225 A | over by 110 A | over by 10 A | none without an upgrade |
Example Problems
Example 1. Standard method, 2020 NEC. A 2,000 square foot home has two small appliance circuits, one laundry circuit, a 12 kW range, a 5 kW dryer, a 4.5 kW water heater, a 2.4 kW dishwasher and disposal pair, and 5 kW of central air conditioning with gas backup heat.
General load: 2,000 x 3 = 6,000 VA, plus 2 x 1,500 = 3,000 VA, plus 1,500 VA, for 10,500 VA connected. Demand: 3,000 at 100 percent plus 7,500 at 35 percent = 3,000 + 2,625 = 5,625 VA. Range: 8,000 VA from Table 220.55 Column C. Dryer: 5,000 VA. Fastened in place appliances: 4,500 + 2,400 = 6,900 VA, and with only three qualifying units the 75 percent factor does not apply. Cooling: 5,000 VA. Total = 5,625 + 8,000 + 5,000 + 6,900 + 5,000 = 30,525 VA. Divide by 240 V to get 127.2 A, so a 150 A service is the smallest standard size that covers it.
Example 2. Same house, optional method. Pool every load except the HVAC into one bucket: 6,000 + 4,500 + 12,000 + 5,000 + 4,500 + 2,400 = 34,400 VA. The first 10,000 VA counts at 100 percent and the remaining 24,400 VA at 40 percent, which is 10,000 + 9,760 = 19,760 VA. Add the air conditioning at 100 percent for 24,760 VA. Divide by 240 V to get 103.2 A, which rounds up to a 125 A service. The optional method lands 24 amps lower on the same house, which is why it is worth running both before you commit to a service size.
FAQ
Which method should you use, standard or optional?
Run both and use the one that fits your project and produces the lower number. The optional method is available when the dwelling is served by a single 120/240 V or 208Y/120 V set of service conductors rated 100 amps or larger. It usually gives a smaller result because it pools the appliance loads before applying the 40 percent factor and it discounts central electric heat to 65 percent. The standard method has no such restriction and is what most inspectors expect on a straightforward gas heated house. Some jurisdictions publish their own worksheet and require it, so check before you submit.
Why is the calculated load so much higher than the electricity actually used?
A load calculation is a worst case capacity check, not a consumption estimate. It assumes the range, dryer, water heater and air conditioner could all be drawing near their nameplate rating at the same moment. Demand factors already shave that down to something realistic, but a house that calculates at 127 amps will typically pull 15 to 30 amps on an average evening. Sizing to average draw would leave no margin for the winter or summer peak that actually stresses the service.
Does a result under 100 amps mean a 100 amp service is enough?
It means 100 amps meets code today. It does not mean 100 amps is the right choice. A 100 amp service leaves very little headroom for an EV charger, a heat pump, an induction range or a hot tub, and each of those additions forces a fresh calculation and possibly a service upgrade that costs far more than sizing correctly the first time. If any electrification is likely within ten years, price the 200 amp option and compare.
Is this calculator a substitute for a licensed electrician?
No. Treat the output as an estimate for planning and budgeting. A permit ready load calculation has to use the NEC edition your jurisdiction has actually adopted, account for local amendments, use real nameplate data from the installed equipment, and be signed by someone licensed to do the work. Use this result to frame the conversation, then have a licensed electrician confirm it before any service, panel or conductor is ordered.