Free Electrical Load Calculator

Estimate the service size a home needs, in amps, using the NEC optional method for dwellings. Enter the floor area and the appliances, and see the calculated load. Free, no signup.

The dwelling

Heated living area, outside dimensions, excluding open porches and unfinished spaces.
Two is the code minimum for kitchen counters. 1500 VA each.

Appliances (nameplate VA)

Well pump, pool pump, hot tub, and anything else permanently connected.
A 40 A charger on a 240 V circuit is 9600 VA. Counted at 125 percent, see below.

Heating and cooling (nameplate VA)

Strip heat that can run with the heat pump.
General loads3 VA per square foot, small-appliance and laundry circuits, appliance nameplates0 VA
After the demand factorFirst 10,000 VA at 100 percent, the remainder at 40 percent0 VA
Heating or coolingThe largest applicable option0 VA
EV charger at 125 percentAdded outside the demand factor as a continuous load0 VA
Calculated load0 VA
At 240 volts0 A
Enter the details above The calculated load is divided by 240 volts, then rounded up to the next standard service size.
This is an estimate, not a permit calculation. It uses the NEC optional method for a single dwelling (Article 220 part IV). The standard method can produce a different figure, and local amendments, existing panel condition, conductor sizing, and the actual nameplate ratings all change the answer. A licensed electrician must run and sign the calculation before any service is sized, ordered, or installed.

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Turn it into an estimate

What this electrical load calculator does

It estimates the total electrical load of a home and converts it into a service size in amps, which is the number that answers the practical question: will a 100 amp panel carry this house, or does it need 200. It uses the optional method for dwellings, which is the calculation most commonly used for a service upgrade on an existing home.

Enter the heated floor area, the appliances that are permanently connected, and the heating and cooling equipment. The result is the calculated load in volt-amps and the service size it rounds up to.

How the optional method works

1. Add the general loads

Three volt-amps for every square foot, 1500 for each small-appliance circuit and the laundry circuit, then the nameplate of every fixed appliance.

2. Apply the demand factor

The first 10,000 volt-amps count in full. Everything above that counts at 40 percent, because a household never runs everything at once.

3. Add the largest of heating or cooling

Heating and air conditioning never run together, so only the larger one counts. Divide the total by 240 volts to get amps.

The parts people get wrong

The demand factor is the first. It is tempting to add up every nameplate and take the total, but that is not the calculation and it will send you to a much larger service than the house needs. The optional method deliberately assumes diversity: the first 10,000 volt-amps at full value and the rest at 40 percent.

Heating and cooling is the second. You do not add them together. The code takes the largest applicable figure, because a house is not heating and cooling at the same moment. Where a heat pump has supplemental strip heat that can run alongside the compressor, both count, at 100 and 65 percent respectively.

EV charging is the third, and it is the one that has changed most recently. A charger is a continuous load, so it is counted at 125 percent of its rating. This calculator adds it outside the demand factor rather than inside, which is the conservative reading and gives the larger number of the two. Your inspector may take the other view, which is one of several reasons the figure here is a starting point rather than an answer.

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Quoting the work that follows

A load calculation is usually the first step in a service upgrade, and the customer's next question is what it will cost. Price the labour with the hourly rate calculator if you are still setting your rate, turn tracked time into billable lines with the billable hours calculator, and send the customer a written estimate with the free quote generator.

Frequently asked questions

It depends on the floor area, the fixed appliances and the heating and cooling equipment, not on the age or the look of the house. Most modern homes calculate out between 100 and 200 amps. Electric heat, a large range and an EV charger are what usually push a house past 100 amps. Run the numbers rather than guessing, then have a licensed electrician confirm them.

Both appear in Article 220. The standard method applies separate demand factors to lighting, ranges and dryers using their own tables. The optional method groups the general loads together and applies one demand factor, which is simpler and is what most service upgrade calculations use. They can give different answers, so a permit calculation should state which method was used.

Because a house does not heat and cool at the same time, so counting both would size the service for a condition that never happens. The optional method takes the largest applicable figure instead. The exception is a heat pump with supplemental strip heat that can run alongside the compressor, where the compressor counts in full and the strip heat at 65 percent.

A charger runs for hours at its full rating, so it is treated as a continuous load and counted at 125 percent. A 40 amp charger on a 240 volt circuit is 9600 volt-amps, which becomes 12,000 in the calculation. This calculator adds that outside the demand factor, which is the more conservative of the two common readings and gives the larger service size.

No. This is an estimating aid for scoping and quoting a job. A permit calculation has to reflect the actual nameplate ratings, the local amendments your jurisdiction has adopted, the condition and rating of the existing equipment, and it has to be run and signed by a licensed electrician. Treat the number here as the starting point for that conversation.

Load calculations are done in volt-amps because that is what the conductors and the service have to carry. For resistive loads such as a water heater or a range the figure matches the wattage, so you can enter the wattage from the nameplate. For motors the two differ, and the nameplate volt-amp rating is the one to use.

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