Quick answer
An electrical load calculation is the code-based estimate of how much power a home or building could draw at one time, used to size the service, panel, feeders and main breaker.
In the US it follows Article 220 of the National Electrical Code. It adds up lighting, appliance and heating or cooling loads, then applies demand factors, because not everything runs at once.
Quick facts
The key facts about Electrical Load Calculation, with sources:
Key takeaways
- A load calculation answers one question: how big must the service and panel be?
- It is not a sum of breaker sizes; demand factors reflect that loads do not all run together.
- The NEC gives a standard method and, for single-family homes, a simpler optional method 2.
- The same house can come out at different sizes under each method 1.
- Run one before adding an EV charger, heat pump, electric range or hot tub.
What a load calculation is
Your home has a fixed amount of power it can pull from the utility. That limit is the service size, such as 100 or 200 amps. A load calculation is how an electrician checks whether the home's likely demand fits under that limit.
It is not a measurement. It is a formula written into the National Electrical Code. It starts with the floor area and the equipment you have, assigns each a value in volt-amperes (VA), then trims the total with demand factors. The result, divided by the voltage, gives amps.
Inspectors ask for one on new homes, service upgrades and big additions. Electricians also use it to decide whether a new Level 2 charger or heat pump circuit fits on the existing service.
How the calculation works
Every method follows the same shape. First, list the loads. General lighting and outlets are counted by floor area, at 3 VA per square foot in the editions our sources cover 1.
Each small-appliance kitchen circuit and the laundry circuit count as 1,500 VA 1. Then add fixed appliances such as a range, dryer, water heater and dishwasher.
Second, apply demand factors. These reflect real use: you rarely run the oven, dryer, AC and water heater at full power at the same moment. The standard method uses separate factors for each group. The optional method uses one blended rule: 100% of the first 10 kVA, then 40% of the rest 2.
Third, add heating or cooling, but only the larger of the two, because they do not run together 1. Finally, divide the total VA by 240 volts to get amps, and round up to the next standard size.
Service amps = (General load after demand factors + Larger of heat or AC) ÷ 240 V
General load- Lighting, outlets, small appliance, laundry and fixed appliances, in VA
Demand factor- Discount for loads that rarely run at once
Heat or AC- Only the larger of the two is counted
240 V- Typical US single-phase home service voltage
Then round up to a standard service size such as 100, 150 or 200 amps.
The methods in NEC Article 220
| Method | Used for | How it handles demand |
|---|---|---|
| Standard method | Any dwelling or building | Separate factors per load type; the first 3,000 VA of general load at 100%, much of the rest at 35% 1 |
| Optional method (220.82) | One dwelling on a single 120/240 V or 120/208 V 3-wire service or feeder of 100 A or more 2 | 100% of first 10 kVA, 40% of the remainder, plus heat or AC at set percentages 2 |
| Existing dwelling method (220.83) | Adding loads to an existing home | Its own optional rules for additions; ask your electrician which applies |
| Feeder and subpanel calculation | A subpanel feeder or detached building | Same Article 220 rules applied to that feeder |
Worked example: one house, two answers
IAEI Magazine ran both methods on the same 2,900 sq ft home 1. These are the article's published figures, written to an earlier NEC edition.
| Item | Standard method | Optional method |
|---|---|---|
| Total calculated load | 47,520 VA | 34,160 VA |
| Amps at 240 V | 198 A | 142 A |
| Service selected | 200 A | 150 A |
| Copper service conductors | 2/0 AWG | 1 AWG |
| Aluminum service conductors | 4/0 AWG | 2/0 AWG |
The optional method gave a smaller result here. The article notes a 200 A service may still be installed for equipment reasons 1. In a much larger 6,000 sq ft example, EC&M's optional calculation reached 89,398 VA, or 372 A, so a 400 A service 2.
Example: what one EV charger adds
An illustration of how a charger enters the standard method under the 2023 NEC. It is not a design for any home.
| Item | Value | Source |
|---|---|---|
| Load counted for EV charging equipment | 7,200 VA, or nameplate if larger | 2023 NEC 220.57 3 |
| Typical home Level 2 charger | Up to 30 A draw, about 7.2 kW | DOE AFDC 4 |
| Current added at 240 V | 7,200 ÷ 240 = 30 A | Arithmetic |
| Fixed-appliance 75% factor | Does not apply to EV charging equipment | 2023 NEC 220.53 3 |
So a home whose calculation already sits close to its service size may not have 30 A to spare. That is where EV load management or a service upgrade come in.
Where load calculations show up
You will see one on a permit application for a service upgrade, a new home, an ADU or a large addition. Electricians attach it so the inspector can check the size of the main breaker and service wires.
It also comes up in quotes. A good EV charger, heat pump or solar quote should say whether the existing service has room. If it does not mention a load calculation, ask for one.
Why a load calculation is worth doing
- Avoids overloads that trip the main or overheat service wires.
- Avoids needless upgrades. Many homes have more room than a breaker count suggests.
- Speeds permits. Inspectors expect it for service work.
- Plans ahead. You can see whether a future EV, heat pump and induction range all fit.
- Compares options. It shows whether load management is enough or an upgrade is needed.
Limits of a load calculation
A load calculation is good at
- Giving a code-accepted size for the service.
- Comparing before and after a new load.
- Being repeatable: two electricians should reach close answers.
A load calculation is not
- A measure of your real bills or usage.
- Exact; the standard method needs judgment calls about which factors apply 2.
- A check on panel condition, wiring age or breaker space.
- Identical across editions; values can change between NEC cycles.
What drives the cost
A load calculation is often part of an electrician's quote or site visit rather than a separate bill.
When it is billed, what drives the cost is the home's size, how many appliances must be listed from nameplates, whether drawings are needed for a permit and whether an engineer's stamp is required for large or commercial work.
The bigger cost question is what the result triggers. Room to spare means a simple circuit. No room means load management or a panel upgrade. Our panel upgrade cost research and the project cost estimator help you plan.
How an electrician runs one
- Measure the floor area from the outside dimensions.
- Read nameplates on the range, dryer, water heater, HVAC and other fixed equipment.
- Add the planned new loads, such as a charger or heat pump.
- Choose the method the code and home allow.
- Apply demand factors and add the larger of heating or cooling.
- Convert to amps and compare with the service, main breaker and service wires.
- Attach the calculation to the permit if work is planned.
You can get a first estimate yourself with the electrical load calculator.
Keeping your calculation current
- Redo it whenever you add a large fixed appliance.
- Keep a copy with your home records and permits.
- Update it after switching from gas to electric heat, cooking or water heating.
- Note your panel label rating and service size alongside it.
Skipping the math can overheat wires
Safety and risk
Adding big loads without a load calculation can push a service past its rating. The first signs are often a main breaker that trips, dimming lights or a warm panel. Do not respond by fitting a bigger breaker. Unplug or turn off the new load and call an electrician.
Signs your service may be over its calculated load
- The main breaker trips when several big appliances run.
- Lights dim across the house when the AC or dryer starts.
- The panel door feels warm or smells of hot plastic.
- A contractor plans a charger or heat pump without asking about service size.
- You have added major electric appliances since the home was built.
The code behind it
Load calculations live in NEC Article 220. States and cities adopt an edition, so the numbers that apply depend on where you live. As of September 2026, 19 states had adopted the 2023 NEC in some form and six the 2026 edition 5.
Optional method. 220.82 applies to a dwelling on a single 120/240 V or 120/208 V three-wire service or feeder of 100 A or more 2.
Heat pumps without backup heat count at 100%, space heating with three or fewer units at 65% 2. EV charging.
The 2023 NEC added 220.57, setting EV equipment at 7,200 VA or nameplate, whichever is larger 3.
The 2023 NEC 220.53 also confirms that the 75% demand factor for four or more fixed appliances does not cover EV equipment 3.
Load calculation vs similar ideas
| Term | What it measures | Used for |
|---|---|---|
| Load calculation | Code-estimated peak demand, in VA or amps | Sizing service, panel and feeders |
| Connected load | Sum of every nameplate | Input to the calculation |
| Kilowatt-hours | Energy used over time | Your bill |
| Overload | Current above a rating for too long | Why a breaker trips |
| Dedicated circuit sizing | One appliance's circuit | Choosing breaker and wire size |
Load calculation myths
- Myth Add up the breakers to get your load.
- Reality Breaker ratings far exceed real demand. Article 220 uses demand factors for that reason 1.
- Myth Every house needs 200 amps.
- Reality Some homes calculate well under it; the IAEI example came out at 142 A under the optional method 1.
- Myth An EV charger always forces an upgrade.
- Reality Only if the calculation shows no room. Load management is another option.
- Myth The calculation is the same everywhere.
- Reality It depends on the NEC edition your area has adopted.
What changes by state
The EV rule in 220.57 exists only in the 2023 and later editions 3, so a home in a state still on an older code may be calculated differently. Licensing rules also decide who may sign a calculation for a permit. Check your state first.
Do you need a load calculation?
If you are adding a large 240-volt load, yes. Start with an estimate, then have an electrician confirm it.
- If Adding an EV charger, heat pump, range or hot tub
- Then Run a load calculation first
- If Calculation shows room to spare
- Then Add a dedicated circuit; no upgrade needed
- If Calculation is close to the service size
- Then Consider load management
- If Calculation exceeds the service size
- Then Plan a service and panel upgrade
Bring nameplates
Photograph the nameplate on each large appliance and the panel label. An electrician can run a much better calculation from those photos.
Questions about Electrical Load Calculation
How do you calculate the electrical load of a house?
You follow NEC Article 220. List general lighting by floor area, add small-appliance and laundry circuits at 1,500 VA each, add fixed appliances, apply demand factors and add the larger of heating or cooling. Divide the total volt-amperes by 240 volts to get amps, then round up to a standard service size.
What is the optional method for a load calculation?
The optional method in NEC 220.82 is a simpler way to size a single dwelling.
It takes 100% of the first 10 kVA of general load and 40% of the rest, then adds heating or cooling at set percentages.
It applies to a dwelling on one 120/240 V or 120/208 V three-wire service of 100 A or more.
Why is my load calculation lower than my breakers add up to?
A load calculation comes out lower because it uses demand factors. Branch breakers are sized for each circuit's worst case, but they never all run at full load together.
The NEC discounts the total to reflect real use, so the calculated load is far below the sum of breaker ratings.
In the IAEI example, a 2,900 sq ft home calculated at 198 amps by the standard method and 142 amps by the optional one 1.
How much load does an EV charger add?
Under the 2023 NEC 220.57, EV charging equipment counts at 7,200 VA or its nameplate rating, whichever is larger. At 240 volts that is 30 amps.
DOE notes a typical home Level 2 charger draws up to 30 amps and delivers about 7.2 kW, on a dedicated 40-amp circuit 4.
The 2023 NEC also keeps EV equipment out of the 75% fixed-appliance discount 3.
Do I need a load calculation for a panel upgrade?
Usually yes. A load calculation shows what service size the home needs and supports the permit. Many inspectors ask for it on service changes.
It also shows if a bigger service is truly needed, or if load management would cover the new load.
Keep a copy with the permit; it saves time the next time you add a big appliance.
Can I do my own load calculation?
You can make an estimate with an online tool to plan and budget. The calculation filed for a permit is normally prepared by the licensed electrician doing the work, because it must use the edition your area adopted and the right nameplate data. Use your estimate to ask better questions.
Is 100 amps enough for a house?
100 amps is enough for some homes and not others; the calculated load decides, not house size alone. A small home with gas heat and cooking may calculate well under 100 amps.
A home with electric heat, an electric range and an EV charger often needs more. A load calculation gives the answer for your home.
Under the optional method, the first 10 kVA counts at 100% and the rest at 40%, which is why many modest all-gas homes fit under 100 amps 2.
Does air conditioning and heat both count in a load calculation?
No, only the larger one counts. The NEC treats heating and air conditioning as noncoincident loads, since they do not run at the same time. The calculation uses whichever is bigger.
Under the optional method, a heat pump without supplemental heat counts at 100%, while space heating with three or fewer units counts at 65% 2.
What happens if my load exceeds my service size?
If the calculated load is larger than the service, the home needs a fix before new loads go on. Options include a service and panel upgrade, load management that limits a charger or other big load, or choosing lower-demand equipment.
An electrician will recommend one based on the numbers. Until then, avoid running the new load alongside other big appliances, and do not fit a larger main breaker to stop trips.
Sources
- IAEI Magazine, "Residential Service Calculations in the National Electrical Code" (2013), retrieved .
- EC&M, "Dwelling Load Calculations Per the National Electrical Code" (2020 NEC basis), retrieved .
- Leviton Captain Code 2023, NEC 220.53 and 220.57 EVSE load calculations, retrieved .
- U.S. DOE Alternative Fuels Data Center, Charging Electric Vehicles at Home and Work, retrieved .
- EC&M, "Wisconsin Adopts 2023 National Electrical Code" (9 September 2026), retrieved .
Expert review
Written by the HyreElectrical Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Method rules and worked figures from IAEI and EC&M code articles; 2023 EV rules via Leviton Captain Code; charger figures from DOE AFDC. Figures shown as examples from named sources. No prices published (G-COST).
Suggest a correction. We fix errors and say what changed.