How to Do a Residential Panel Load Calculation
Why the optional method is the one you will use
NEC Article 220 gives two ways to figure the load on a dwelling service. The standard method in Part III (220.40 and following) works for any building and goes line by line through lighting demand factors, appliance demand factors, Table 220.55 for ranges and Table 220.54 for dryers. The optional method in 220.82 is for a single-family dwelling, or one unit of a multifamily building, served by a 120/240 V or 208Y/120 V three-wire service or feeder of 100 A or more, and it collapses most of that into a single demand factor. It is faster, it is what most inspectors expect to see for a house, and it usually comes out a little lower. This guide uses the 2023 NEC. The numbers in 220.82 have not changed in recent editions, but your adopted edition, local amendments and the AHJ govern.
Step 1: add up the general loads
220.82(B) has you total the following, at nameplate or at the stated unit values:
- 3 VA per square foot of floor area, using the outside dimensions of the house and leaving out open porches, garages and unfinished space that is not adaptable for future use.
- 1,500 VA for each 20 A small-appliance circuit (210.11(C)(1) requires at least two) and 1,500 VA for the laundry circuit.
- The nameplate rating of every fixed appliance: range, wall oven, cooktop, dryer, water heater, dishwasher, disposal, a microwave on its own circuit, a well pump, and so on. Use nameplate, not the demand tables; the optional method does its own discounting.
- The nameplate of any permanently connected motor not already counted.
Leave air conditioning and electric heat out of this list. They are handled separately in Step 3. The panel load calculator follows these same lines if you would rather fill in boxes than add columns.
Step 2: apply the demand factor
Take 100% of the first 10,000 VA and 40% of everything over 10,000 VA. The reasoning is plain: the range, the dryer and the water heater are not all on at once, and the longer the list, the less of it runs together. This one factor replaces the lighting, appliance, range and dryer demand tables of the standard method.
Step 3: add the larger of cooling or heating
220.82(C) adds the largest of several heating and cooling loads, because the air conditioner and the furnace do not run at the same time. The two cases you will see most are 100% of the air-conditioning nameplate and 65% of a central electric space-heating system, or 65% of fewer than four separately controlled heating units; four or more separately controlled units, such as baseboard heaters in every room, are taken at 40%. A heat pump with supplemental strip heat is 100% of the compressor plus 65% of the strips unless the controls keep the two from running together. Compare the candidates and keep the biggest one.
Worked example: a 2,000 square foot house
| Load | VA |
|---|---|
| General lighting and receptacles, 2,000 sq ft × 3 VA | 6,000 |
| Two small-appliance circuits × 1,500 VA | 3,000 |
| Laundry circuit | 1,500 |
| Range (nameplate) | 12,000 |
| Dryer | 5,000 |
| Water heater | 4,500 |
| Dishwasher | 1,200 |
| Disposal | 900 |
| General load total | 34,100 |
Demand: 10,000 + 0.40 × 24,100 = 19,640 VA. The house has a 5,000 VA air conditioner and 7,000 W of central electric heat. The heat counts at 65%, which is 4,550 VA, so the air conditioner at 5,000 VA is larger and is the one added: 19,640 + 5,000 = 24,640 VA. Amps = 24,640 ÷ 240 = 102.7 A. That is over 100 A, so the next standard rating is a 125 A service. In practice most electricians would install 150 A or 200 A here. The cost difference is small, 230.79(C) already sets 100 A as the floor for a one-family dwelling, and the first EV charger, counted at 7,200 VA or nameplate under 220.57, or the first heat pump pushes the number up fast. Service equipment is bought in standard ratings, so a 102.7 A result and a 124 A result land on the same panel.
The standard method, existing dwellings and why 200 A is common
Use the standard method (220.40) when the dwelling does not qualify for 220.82: a service under 100 A, a feeder that serves more than one unit, or an AHJ that asks for it. It takes the general lighting at 3 VA per square foot with the first 3,000 VA at 100% and the next block at 35%, ranges through Table 220.55 (one 12 kW range counts as 8 kW), dryers through Table 220.54 at 5,000 W or nameplate, 75% of four or more other fixed appliances (220.53), the larger of heating or cooling (220.60), and 25% of the largest motor. It is longer, and on the same house it usually lands a little higher.
For an existing dwelling getting a new load, 220.83 is the tool: 100% of the first 8,000 VA and 40% of the remainder of the existing and new loads; where new air conditioning or electric heat is being added, that equipment goes in at 100% on top of the 8 kVA and 40% figure for everything else. That is the calculation you do before adding a 48 A EV charger to a 100 A panel, and it is why so many of those jobs end in a 200 A upgrade. Once the service rating is set, 310.12 lets a one-family dwelling service use conductors at 83% of the rating, which is how 4/0 aluminum or 2/0 copper serve a 200 A service; the wire size calculator handles the feeders and branch circuits downstream. If a standby generator is part of the plan, the same demand numbers feed the generator sizing calculator. Voltbox keeps the load calculation and wire size tools together offline, and load calculations are a standard question on the electrician practice exam.
Step by step
- Total the general loads3 VA per square foot of floor area, 1,500 VA for each small-appliance circuit and the laundry circuit, and the nameplate of every fixed appliance and motor (220.82(B)).
- Apply the demand factorTake 100% of the first 10,000 VA plus 40% of the remainder.
- Add heating or coolingAdd the larger of 100% of the air-conditioning nameplate or 65% of central electric space heating (220.82(C)); four or more separately controlled heating units are taken at 40%.
- Convert to ampsDivide the total VA by 240 for a 120/240 V single-phase service.
- Pick the service sizeRound up to the next standard rating (100, 125, 150, 200 A), never below 100 A for a one-family dwelling (230.79(C)), and leave headroom for EV charging and heat pumps.
Frequently asked questions
What size electrical service does a 2,000 square foot house need?
With a 12 kW range, a dryer, a water heater and 5,000 VA of air conditioning, the 220.82 optional method comes to about 103 A, so 125 A is the smallest standard size. Most new houses get 200 A for EV charging and heat pumps.
Do I use the nameplate or the demand table for the range in the optional method?
Nameplate. The optional method applies its own 40% factor to everything over 10 kVA instead of Table 220.55. The range tables belong to the standard method.
Does the garage count in the square footage?
No. 220.82(B) uses the outside dimensions of the house but excludes open porches, garages and unfinished space that is not adaptable for future use.
Which method do I use to add an EV charger to an existing house?
220.83, the optional method for existing dwellings: 100% of the first 8 kVA and 40% of the remainder of the existing plus new loads, with the EVSE counted at 7,200 VA or nameplate, whichever is larger (220.57).
Written by TapForge Studios, a one-person Android studio run by a tradesman with a background in electrical, HVAC and life-safety work. Reviewed October 7, 2026. This guide is general information, not engineering, legal or tax advice; the adopted code edition, the manufacturer's instructions and the authority having jurisdiction govern.
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