About the Home Electrical Load Calculator
This home electrical load calculator estimates the minimum service size a single-family dwelling needs, using the optional (simplified) method in NEC Section 220.82, which the International Residential Code reproduces as Table E3602.2 (quoted here from the freely published 2012 IRC). The 2026 NEC, the current edition, continues a reorganization of the code, so section numbers in the edition your area has adopted may differ even where the method is the same. Enter the floor area, the number of 20-amp kitchen and laundry circuits, the nameplate ratings of fixed appliances such as the range, dryer, water heater and EV charger, and your heating and air-conditioning equipment.
It is useful when you are adding a heat pump, an EV charger, a hot tub or an addition and want to know whether a 100 A or 150 A panel is still enough, or when comparing a quote for a 200 A service upgrade. The result is the calculated load in volt-amperes and amps at 240 V, and the next standard service rating above it.
This is a planning estimate, not a permit calculation. The optional method applies to a dwelling unit served by a single 120/240 V, 3-wire service of 100 A or more; your electrician or inspector may use the standard method, local amendments or newer NEC editions, and existing services can also be sized from a year of utility demand data (NEC 220.87).
With the default inputs, the calculated service load is 103.7 A. Change any value above to recalculate instantly.
How to use the home electrical load calculator
- 1Enter the finished living area of the home.
- 2Count the 20 A kitchen small-appliance and laundry circuits (minimum three).
- 3Enter nameplate kW for the range, dryer, water heater and other fixed appliances (0 for gas units).
- 4Add any EV charger and the air-conditioning nameplate rating.
- 5Choose the type of electric heat and its rating, then read the amps and service size.
Formula and method
The optional method in NEC 220.82 (IRC Table E3602.2) starts with general loads: 3 volt-amperes per square foot for lighting and general-use receptacles, 1,500 VA for each 20 A small-appliance and laundry circuit, and the nameplate rating of every fastened-in-place or dedicated-circuit appliance such as ranges, ovens, dryers, water heaters and EV chargers. The first 10,000 VA of that subtotal counts at 100% and everything above it at 40%, reflecting that not everything runs at once.
Then the single largest heating or cooling item is added: 100% of air-conditioning, 100% of a heat pump without supplemental heat, 100% of the heat pump compressor plus 65% of supplemental heat (or just 65% of the supplemental heat when the compressor is interlocked so both cannot run together), 65% of electric space heat with fewer than four separately controlled units (including a central furnace), 40% with four or more units, or 100% of thermal-storage or continuously loaded heat. For an interlocked heat pump this calculator conservatively uses the larger of the compressor rating and 65% of the backup heat. The total in VA divided by 240 V gives the minimum service ampacity.
- A
- Floor area in square feet
- n
- Number of 20 A small-appliance and laundry circuits
- G
- General load subtotal in VA
- D
- General load after demand factors
- HVAC
- Largest of the heating or cooling items
- I
- Calculated load in amps at 240 V
Worked examples
2,000 sq ft all-electric kitchen, gas heat, 5 kW AC
General loads are 6,000 VA lighting + 4,500 VA for three circuits + 24,200 VA of appliances = 34,700 VA. The first 10,000 VA counts fully and 40% of the remaining 24,700 VA adds 9,880 VA, for 19,880 VA. Adding 5,000 VA of AC gives 24,880 VA ÷ 240 = 103.7 A, so a 125 A service is the next standard size.
Adding a 48 A EV charger and heat pump with strips
The EV charger raises general loads to 46,200 VA, which demand-factors to 10,000 + 0.4 × 36,200 = 24,480 VA. Heat pump plus 65% of 10 kW strips is 11,500 VA, larger than the 5,000 VA AC. The total of 35,980 VA is 149.9 A — just inside a 150 A service.
Small gas home, 1,200 sq ft
With gas cooking, drying and water heating the general load is 3,600 + 4,500 + 2,000 = 10,100 VA, which becomes 10,040 VA after demand. Adding 3,500 VA of AC gives 13,540 VA or 56.4 A, but the code minimum for a single-family service is still 100 A.
Frequently asked questions
How do I know if my house needs a 200 amp panel?+
Run a load calculation like this one: if the calculated load exceeds about 150 A, or you plan large additions such as an EV charger, heat pump with backup strips or a hot tub, a 200 A service is usually the next step. Many new all-electric homes are built with 200 A as a baseline.
What is the NEC optional method for dwellings?+
NEC 220.82 is a simplified calculation for a single dwelling unit with a 120/240 V service of 100 A or more. It totals general loads, takes 100% of the first 10 kVA and 40% of the rest, then adds the largest heating or cooling load.
Why does the calculation only count the larger of heating or cooling?+
Heating and air-conditioning do not run at the same time, so the NEC treats them as noncoincident loads and adds only the larger one to the service calculation.
What is the minimum service size for a house?+
The NEC and the IRC require a 100 A, 3-wire service for a one-family dwelling, regardless of how small the calculated load is.
How many amps does an EV charger add?+
A Level 2 charger is counted at its nameplate rating: a 32 A charger is about 7.7 kW and a 48 A charger about 11.5 kW. Because it falls in the general load above 10 kVA, the optional method counts only 40% of it, roughly 13 A or 19 A at 240 V.
Can I use my electric bill instead of a load calculation?+
For an existing home, NEC 220.87 lets you size added load from the maximum demand recorded over a year of utility data: 125% of that peak demand plus the new load must fit within the existing service rating. Your electrician can request this data from the utility.