Electrical Load Calculator for Homes
Add the appliances in your home or on a circuit to see the total load in watts, the realistic peak when not everything runs at once, the current in amps, and the breaker, service and generator size that fit. Switch to the NEC tab to size a house service with the 220.82 optional method used for permits.
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This calculator gives an estimate for planning only. Electrical work must follow your local wiring rules and be checked by a qualified electrician.
How to use it
- Choose your supply, for example 120/240 V in the US.
- Edit the appliance list: pick each appliance, check the watts on its label and set how many you have.
- Choose how much of it runs at the same time. Typical homes are around 50%.
- Read the peak load, amps, breaker and generator size, or switch to the NEC tab for a permit-style service calculation.
Why use this tool
Appliance list with typical watts
Thirty common appliances fill in their usual wattage and hours, and you can change any number.
Realistic peak, not just a sum
The largest load counts in full and a share of the rest runs with it, as in standard diversity methods.
Breaker, service and generator
Amps at your voltage, the next breaker size up with a 125% margin, the US service size and a generator that covers motor start-up.
NEC 220.82 optional method
Lighting at 3 VA per square foot, kitchen and laundry circuits, fixed appliances and the larger of heating or cooling.
Energy and cost
Hours of use turn into kWh per day and month and a monthly bill at your electricity rate.
Any country
120/240 V, 230 V, 400 V three-phase, 220/380 V and Japan's 100 V are all built in.
How to calculate the electrical load of a house
Start with the connected load: the nameplate watts of every appliance added together. A typical American home easily reaches 30 to 40 kW connected, yet the panel rarely sees more than a third of that, because the range, dryer, water heater and air conditioner seldom all run at full power at the same moment.
Load calculations account for this with a demand or diversity factor. This calculator counts the largest appliance in full and adds a share of everything else. To turn watts into amps, divide by the voltage: amps = watts ÷ volts, or watts ÷ (1.73 × volts) for three-phase.
| Appliance | Typical watts | Amps at 240 V |
|---|---|---|
| Electric range | 8,000 to 12,000 W | 33 to 50 A |
| Clothes dryer | 5,000 W | 21 A |
| Electric water heater | 4,500 W | 19 A |
| Central AC (3 ton) | 3,500 W | 15 A |
| Level 2 EV charger | 7,200 to 11,500 W | 30 to 48 A |
| Heat pump (3 ton) | 3,000 to 4,000 W | 13 to 17 A |
What size electrical service do I need?
Most new single-family homes in the US get a 200 A service. 100 A is enough for a small gas-heated home; all-electric homes with a heat pump, electric range and an EV charger often need 200 A, and large homes with two EVs or electric resistance heat move to 320/400 A.
Before adding a big load such as an EV charger or a heat pump to an existing panel, electricians check the calculated load against the service rating. If the new total stays under 80% of the service, it usually fits; otherwise a load management device or a service upgrade is needed.
The NEC 220.82 optional method, step by step
- General lighting and receptacles: 3 VA for each square foot of living area.
- Kitchen small-appliance circuits and laundry: 1,500 VA per circuit.
- Fixed appliances (range, dryer, water heater, dishwasher, EV charger) at their nameplate rating.
- Take the first 10,000 VA of that total at 100% and the remainder at 40%.
- Add the largest of: air conditioning at 100%, central electric heat at 65%, or four or more separately controlled heaters at 40%.
- Divide the total by 240 V to get the minimum service current.
Sizing a generator or battery inverter
A generator must cover the running load plus the brief surge when a motor starts. Refrigerators, well pumps and air conditioners can draw about three times their running power for a second. The calculator adds that surge for the largest motor and a 25% margin, and gives the result in kVA, the rating printed on generators.
Frequently asked questions
How do I convert watts to amps?
Divide watts by volts. A 1,500 W heater on 120 V draws 12.5 A; a 4,500 W water heater on 240 V draws 18.75 A. For three-phase, divide by 1.73 × volts.
Is a 100 amp service enough for a house?
For a small home with gas heat, cooking and hot water, usually yes. Homes with an electric range, dryer, water heater and central AC typically calculate above 100 A and need 150 or 200 A.
How many amps does an EV charger need?
A Level 2 charger rated 7.2 kW draws 30 A on a 40 A circuit; an 11.5 kW unit draws 48 A on a 60 A circuit. Chargers count at 100% in a load calculation because they run for hours.
What is a demand or diversity factor?
It is the share of the connected load that is likely to run at the same time. Codes build it in so that services are not sized for the impossible case where everything is on at once.
Why size a breaker at 125% of the load?
Breakers are rated to carry 80% of their value continuously. Dividing by 0.8, or multiplying by 1.25, keeps a continuous load from tripping it or overheating the wiring.
Can I use this for a permit?
Use it to check your numbers. Permit applications need the calculation your local code adopts, and the final design should be checked by a licensed electrician.
Residential load calculation, worked through
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