An electrical load calculation adds up the power your home could demand at its busiest, then checks that total against what your electrical service and panel can supply. For most existing houses in the U.S., the method is the optional calculation in NEC Article 220.82: count lighting and receptacles at 3 VA per square foot, add the kitchen and laundry circuits, add fixed appliances, apply demand factors, then divide the total VA by 240 V to get amps. This guide walks through each step with a worked example, shows where EV chargers and HVAC fit, and explains when the numbers should be checked by a licensed electrician.
TL;DR
- Load is what your home draws. Capacity is what the service, panel and wiring can safely deliver. The calculation compares the two.
- The 220.82 method: 3 VA per square foot, 1,500 VA per small-appliance circuit, nameplate loads for fixed appliances, 100% of the first 10,000 VA and 40% of the rest, then the larger of heating or cooling.
- Divide total VA by 240 V. The service rating has to be equal to or greater than that result.
- An EV charger counts at 7,200 W or its nameplate rating, whichever is larger, and an empty breaker slot does not prove you have the capacity.
- Use the worksheet to plan. Have an electrician confirm it before you add a big load or upgrade a panel.
Table of Contents
- Load vs. capacity: the difference that matters
- The basic math: watts, volts and amps
- How to calculate your home's electrical load, step by step
- A worked example
- Which loads belong on the worksheet
- EV chargers and the load calculation
- When the calculation says you have room, and when it does not
- Which code and who checks it
- Our perspective: why we start with photos and a conversation
- Get your load checked by a local electrician
- When to call a professional
- FAQ
- Sources
Load vs. capacity: the difference that matters
Load is the power used by appliances, equipment and other connected devices. Capacity is the maximum the service, panel, circuit or system can handle. What is left after your peak load is your available capacity, as Seattle City Light explains.
Two misunderstandings cause most of the trouble:
- Breaker space is not capacity. The breakers in a panel can add up to more than the panel's rating, because appliances do not all run at once. The Department of Energy's BENEFIT factsheet draws this distinction directly. A panel with open slots can still be out of capacity.
- A bigger panel is not always the fix. Sometimes the calculation shows you already have room. Sometimes it shows you are close to the limit and one new appliance tips it over. You only know by doing the math.
You can find your service size on the utility meter label, the panel label or the main breaker, according to the same DOE factsheet. Common residential sizes are 100, 150 and 200 amps.
The basic math: watts, volts and amps
Everything in the calculation rests on one relationship. Power in watts equals voltage times current in amps, so amps equal watts divided by volts. The DOE factsheet applies this to a whole home by dividing the total load by 240 V to estimate amperes.
A quick example: a 5,000 VA electric dryer on a 240 V circuit draws about 5,000 / 240 = 20.8 A. The calculation treats volt-amperes (VA) and watts as close enough for planning, and uses the nameplate rating printed on the appliance wherever it is available.
How to calculate your home's electrical load, step by step
There are two NEC methods you will hear about. The standard method in Part III of Article 220 is more detailed. The optional method in 220.82 is the one most worksheets for single-family homes use. The Minnesota ASHP Electrical Service & Panel Evaluation Guide lays out the 220.82 sequence, and the steps below follow it.
Step 1: General lighting and receptacle load
Measure the living area using the outside dimensions of the home, without the garage or unfinished spaces. Multiply the square footage by 3 VA. A 2,800-square-foot house gives 8,400 VA.
Step 2: Small-appliance and laundry circuits
Add 1,500 VA for each small-appliance circuit. Kitchens need at least two, and the laundry circuit is another 1,500 VA. Three circuits give 4,500 VA. This is how the City of Carmel-by-the-Sea worksheet handles it.
Step 3: Fixed appliances at nameplate values
Add the nameplate ratings of appliances that are wired in place: range, water heater, dryer, dishwasher, disposal and the like. Read the label on the appliance, not a catalog estimate. If you are sizing a new water heater, our neighbors in the trades have a useful explanation of sizing a water heater by peak hour, which helps you pick a unit before you read its electrical nameplate.
Step 4: Apply the demand factors
Not everything runs at once, so the method discounts the total. Take 100% of the first 10,000 VA of the general load and 40% of whatever is left. The Minnesota ASHP guide and the DOE Building Science Education problem set both use this split.
Step 5: Add heating or cooling, whichever is larger
Heating and air conditioning are not added together. You take the larger of the two (the heating at 100% in the DOE exercise) and add it to the result of Step 4. Heat pumps, electric furnaces and strip heat can be big numbers, so read their nameplates carefully.
Step 6: Convert to amps and compare
Divide the total VA by 240 V. The service rating must be greater than or equal to the calculated service load.
A worked example
The Carmel worksheet uses a 2,800-square-foot home with these inputs:
| Load | VA |
|---|---|
| Area load (2,800 sq ft x 3 VA) | 8,400 |
| Three small-appliance and laundry circuits | 4,500 |
| Range | 14,000 |
| Water heater | 3,000 |
| Dryer | 5,000 |
| Dishwasher | 1,500 |
| Connected general load | 36,400 |
In that example, the first 10,000 VA counts in full. The remaining 26,400 VA is multiplied by 40%, which is 10,560 VA. Add the 10,000 back and the demand-adjusted general load is 20,560 VA.
Now add the loads that matter in a coastal Carolina house. These next figures are our own illustration of the method, not a published example, so treat them as a planning sketch:
- Add a Level 2 EV charger at 7,200 VA to the 36,400 VA. The general load becomes 43,600 VA. The first 10,000 counts fully, and 33,600 x 40% is 13,440, for 23,440 VA. Divided by 240 V, that is about 97.7 A.
- Add a 6,000 VA heating load at 100% (the larger of heating or cooling). The total is 29,440 VA, or about 122.7 A.
That house fits on a 150 A or 200 A service with room to spare. It would not be a comfortable fit on a 100 A service. The exact way each load is classified is a judgment your electrician makes, which is why the answer should be verified before work begins.
For reference, Carmel's own full example, with all its inputs, divides 30,310 VA by 240 V and arrives at roughly 126 A as the minimum panel capacity.
Which loads belong on the worksheet
A complete worksheet includes:
- Area lighting and general-use receptacles.
- Kitchen small-appliance circuits and the laundry circuit.
- Fixed appliances at nameplate values.
- Heating or air conditioning.
- EV supply equipment (EVSE).
The Carmel worksheet covers those, and the South Lake Tahoe worksheet adds ranges, ovens, dryers, other loads and 25% of the largest motor.
Lighting upgrades are rarely the problem, since LED loads are small, but they do change how a room is used. If you are planning layered fixtures, this overview of indirect lighting for home and office shows the kinds of additions that end up on your circuit list. Pools, hot tubs, well pumps, workshops and detached garages are the loads people forget, and they can be large.
EV chargers and the load calculation
An EV charger is often the reason people search for this topic. Three points are worth knowing:
- It counts at least 7,200 W. NFPA says that for service-load calculations EVSE is calculated at 7,200 W or its nameplate rating, whichever is larger. Article 625 holds the main installation rules.
- It is a continuous load. The Department of Energy's Alternative Fuels Data Center says home charging is a continuous load under the NEC, and that installations must follow local and state codes, with permits possibly required. This is where the "1.25 rule" comes in: the circuit is sized at 125% of the charger's continuous current. We explain it in our EV charger load calculation guide.
- An open slot proves nothing. NREL's electrical contractor handbook says Level 2 home charging commonly draws 30 to 80 A continuously, and that a site assessment and load calculation are required when deciding whether an upgrade is needed.
For wire and breaker sizing by charger amperage, see our guide to Level 2 charger wiring. If you are charging two cars, dual EV charger installation changes the math, and condo owners face extra approvals covered in our condo EV charging guide.
When the calculation says you have room, and when it does not
If your total amps are comfortably below the service rating, you can usually add the new load without upgrading. If the result is close or over, you have a few options:
- Use measured data instead. NEC 220.87 lets you use a year of utility demand records. The DOE factsheet describes multiplying maximum annual demand by 125% and dividing by 240 V to estimate existing ampacity. If the total with the new load stays below panel ampacity, no upgrade is needed. Specific conditions apply, so this is a job for a professional.
- Manage the load. Some chargers and panels can limit their draw so the total stays within capacity. Ask an electrician what your equipment and local rules allow.
- Upgrade the service. If the numbers do not work, a larger panel or service is the answer. See our panel upgrade cost breakdown, our panel upgrades and our 400-amp service work for large homes.
Which code and who checks it
The NEC is published by NFPA as NFPA 70. ICC describes the 2023 edition as the authoritative U.S. document for electrical installations, and notes that it includes load-calculation requirements for outlets supplying EVSE. States and local jurisdictions adopt specific editions and add amendments, so the edition that applies to your permit is set by your local building department, not by this article. Ask them which one governs before work starts.
Our perspective: why we start with photos and a conversation
Most load problems we see do not come from bad math. They come from missing information: an undocumented sub-panel, a hot tub nobody mentioned, a nameplate that is hidden behind a washer. A worksheet is only as good as its inputs.
That is why our consultations begin with what you already have. Send us photos of your panel, the meter, the appliance labels and the spot where you want the new equipment. We can usually tell you whether the calculation is likely to pass, what we need to measure on site, and whether you should expect a panel conversation at all. We would rather tell you a panel upgrade is not needed than sell you one.
We also think the calculation belongs in writing. You should leave the conversation knowing the numbers, the assumptions and the reason for our recommendation, not just the price.
— Logan
Get your load checked by a local electrician
If you are planning an EV charger, a panel upgrade, a kitchen remodel, a generator connection or a home addition in the Myrtle Beach area, we will run the calculation with you. We offer free estimates, and you can send photos ahead of time to speed up planning. See our electrical services or go straight to EV charger installation in Myrtle Beach.
For existing commercial buildings, commercial panel upgrades start with the same type of load study.
When to call a professional
The worksheet is a fine way to understand your home. These are the situations where you should have a licensed electrician and your local building department involved:
- You are adding an EV charger, heat pump, electric range or spa. Electricians can tell you whether your home has adequate capacity, and permits may be required.
- Your breakers trip, lights dim or the panel is warm. Those are signs of a problem, and a calculation will not solve it. Book repairs and troubleshooting.
- You have a commercial property. Seattle City Light recommends a load study before adding load, reviewing equipment nameplates, proposed equipment, square footage and occupancy hours.
- You are remodeling or building new. Plan the load before the walls are closed. Our remodel and construction services include this planning.
Do not open the panel and work inside it yourself. Service conductors stay energized even with the main breaker off.
FAQ
How do I calculate my home's electrical load?
Multiply your living area by 3 VA per square foot, add 1,500 VA for each small-appliance and laundry circuit, and add the nameplate ratings of fixed appliances. Apply 100% to the first 10,000 VA and 40% to the rest, add the larger of heating or cooling, and divide by 240 V. The result is your calculated service load in amps.
What size service does a typical house need?
It depends on the home's size, appliances and heating. In the Carmel example, the minimum came out near 126 A, which would exceed a 100 A service. Your own worksheet gives the real answer, and an electrician should confirm it.
Can I add an EV charger if my panel has an open slot?
Not on that basis alone. NREL says an open slot does not prove adequate service, and a load calculation is required to decide whether an upgrade is needed. A Level 2 charger commonly draws 30 to 80 A continuously.
What is the difference between 220.82 and 220.87?
Article 220.82 is a calculation from your home's size, circuits and appliances. Article 220.87 uses a year of measured maximum demand from utility records, with specific conditions. Both are described in the Minnesota ASHP guide and the DOE factsheet, and an electrician decides which fits your home.
Sources
- Capacity, Load and Electrical Service, Seattle City Light
- BENEFIT Factsheet: Home Electrification and Electric Panel Upgrades, U.S. Department of Energy
- Electrical Service & Panel Evaluation Guide, Minnesota ASHP
- Electrical Panels Problem Set 3.1, DOE Building Science Education
- Electrical Panel Calculations job aid, City of Carmel-by-the-Sea
- NEC Load Calculations worksheet, City of South Lake Tahoe
- EVs and Parking Garages, NFPA
- Charging Electric Vehicles at Home, Alternative Fuels Data Center
- Electric Vehicle Handbook for Electrical Contractors, NREL
- NFPA 70: National Electrical Code, 2023 Edition, ICC