Free tool · no sign-up · tiny homes to full homes
Electrical load calculator & panel schedule.
Size your service the way the code does (NEC 220.82), lay out every breaker on a panel you can print, and find out before you buy whether the espresso machine and the kettle can share an outlet.
- ✓ NEC 2023 service calc
- ✓ Printable panel schedule
- ✓ Circuit check (80 % rule)
- ✓ EV, heat pump & induction ready
- ✓ Optional solar sizing
- ✓ Shareable link
The guide
How a home’s electrical load is calculated
The National Electrical Code gives two ways to size a dwelling’s service. The optional method (220.82) is the one most electricians and plan reviewers use for a single home because it is short and slightly conservative. It adds a general allowance of 3 VA for every square foot (lights and ordinary outlets), 1,500 VA for each kitchen small-appliance circuit and the laundry circuit, and the nameplate rating of everything fastened in place: range, ovens, water heater, dryer, dishwasher, pumps, and an EV charger. Because not everything runs at once, the first 10,000 VA counts in full and everything above it counts at 40 percent. Heating and cooling are added last, at the largest of a few options (air conditioning at 100 percent, electric heat at 65 percent, and so on). Divide by 240 volts and you have the load in amps; the service is the next standard size up, never less than 100 A.
Why older homes run out of room
A house wired in the 1960s or 70s often has a 100 A service and a panel with 20 spaces, sized for a gas range, a gas water heater and window units. Add a heat pump, an induction range, a tankless water heater and a Level 2 EV charger and the same house calculates well above 150 A. The panel runs out of spaces before the service runs out of amps, and the combination is the most common reason a kitchen or garage remodel turns into a service upgrade. Running the numbers before the cabinets are ordered is the cheap part.
The breaker that tripped every Saturday
Our own first office was a bedroom in an older house: two PCs, two monitors, a laser printer, the router, a space heater in winter, and a PlayStation for the two of us to play side by side on the weekend. All of it on one 15 A bedroom circuit that also fed the hallway. It held until the printer warmed up or the heater kicked on, then tripped, and the fix for a while was an extension cord from the room next door. That is not a fix, it is a fire-risk workaround, and it is exactly what the circuit check above is for: list what runs together, see the percentage, and move the heater or the printer to a different circuit (or give the office its own 20 A).
Reading the panel schedule
The drawing mirrors a real load center. Odd-numbered breakers go down the left, even down the right, and each pair of rows alternates between the two hot legs (A and B) of the service. A 240 V appliance uses a 2-pole breaker that spans two slots in one column, so it touches both legs. The calculator balances 120 V circuits across the legs and warns when one side carries much more than the other. Colors mark GFCI (ground-fault), AFCI (arc-fault) and dual-function breakers; kitchens, laundry, bathrooms, garages and outdoor outlets need ground-fault protection, and most living areas need arc-fault protection under current code.
What this calculator simplifies
- Library wattages are typical; the nameplate on your appliance governs. Motor loads (pumps, compressors) are entered as nameplate VA rather than full-load amps from the NEC tables.
- Breaker sizes follow the common pairing for each appliance; the installer confirms them against the manufacturer’s minimum circuit ampacity and maximum overcurrent protection.
- Circuit counts for lights and receptacles are a planning estimate (one 15 A circuit per roughly 480 ft²); the real count depends on room layout and the required receptacle spacing.
- The circuit check treats watts as volt-amps and assumes the loads run at the same moment; motors and laser printers draw more for a second at startup.
- Feeder and conductor sizing, voltage drop, multifamily demand factors and the standard (220.40) method are outside the tool.
Questions
Is this calculator only for tiny homes?
No. It started as a tiny-home tool and still has a tiny home preset, but the method (NEC 220.82, the optional calculation for a dwelling unit) is the same one used for any single-family home, ADU or container home. Pick the preset closest to your project and edit from there.
How accurate is the service size?
The arithmetic follows NEC 2023 Article 220 Part IV exactly: 3 VA per square foot, 1,500 VA per small-appliance and laundry circuit, nameplate ratings for fixed appliances, the first 10 kVA at 100 percent and the rest at 40 percent, plus the largest heating or cooling load. Accuracy depends on your inputs: use the nameplate on each appliance, not the library default, and the result matches what an electrician or plan reviewer would calculate by hand.
Why don’t my espresso machine or gaming PC change the service size?
Plug-in loads are already covered by the 3 VA per square foot and the small-appliance circuits in the code method, so they don’t add to the service calculation. They do trip breakers, though, which is what the circuit check is for: it adds up everything running on one outlet circuit and compares it with the breaker and the 80 percent rule.
What is the 80 percent rule?
A breaker is designed to carry its full rating briefly, but a load that runs three hours or more (continuous) is limited to 80 percent of the rating, and a single plug-in appliance cannot exceed 80 percent of the circuit either (NEC 210.23). On a 15 A circuit that is 1,440 W; on a 20 A circuit, 1,920 W. One espresso machine already uses most of a 15 A circuit.
Can I use the panel schedule for my permit?
It is a planning document. Most building departments accept a load calculation prepared by the electrical contractor or an engineer; some ask for it on their own form. Print this one and hand it to your electrician as the starting point, or send the .json file with our intake if you want the engineering done.
Does it do solar and batteries?
Turn on “Off-grid / solar sizing” and enter hours per day for each load. You get daily kWh, a solar array size for your peak sun hours, an inverter size and a battery bank size. For run-time scenarios use the battery calculator; for the structural side of a roof array, that is a service we offer.
Which code edition?
NEC 2023. Florida adopts the NEC through the Florida Building Code with amendments; other states adopt different editions on their own schedule. The service calculation in 220.82 has been stable across recent editions, so the result is the same under 2017 and 2020 for the loads here.
Remodeling or building?
Put the electrical plan on the drawings.
Sealed plans for remodels, additions, ADUs and new homes, with the panel location, dedicated circuits and service size noted where the plan reviewer looks for them. Custom quote.