Home Panel Load Calculator (NEC 220.82)

Electrical panel load calculation determines whether your existing service panel can handle your home’s electrical demands. Most residential panels are rated at 100A, 150A, or 200A service. If your calculated load approaches or exceeds the panel rating, you need an upgrade.

This page builds the load from scratch using the NEC optional method, so all you need is the square footage and the appliance nameplates. If you already have a total load in kilowatts and only want to know what is left, the panel capacity and headroom calculator answers that in two fields.

Why the percentage here is against the full rating, not 80%. The 80% figure belongs to continuous loads on a device that has not had demand factors applied. Article 220.82 has already applied them, at 100% on the first 10 kVA and 40% on the rest, so its answer is compared to the service size directly. Discounting it again by 80% would be counting the same diversity twice. The chart below still draws the 80% line, because it is a sensible planning target for anyone about to add an EV charger, but the compliance comparison is the full rating.

NEC optional dwelling load calculation (Article 220.82):

Step 1: General lighting and receptacle load: Square footage × 3 watts per sq ft (NEC Article 220.12)

Step 2: Small appliance circuits: Add 1,500W for each required small appliance circuit (kitchen: 2 circuits minimum = 3,000W)

Step 3: Laundry circuit: Add 1,500W for one laundry circuit

Step 4: Fixed appliances (nameplate wattage): Add actual wattage for each appliance fastened in place or on its own circuit:

• Electric range: 8,000–12,000W (use nameplate)
• Electric dryer: 5,000–6,000W
• Water heater: 3,500–5,500W
• Pool pump: 750–2,000W

Step 5: Apply the demand factor to that subtotal: The first 10,000W: use at 100% Remaining watts: multiply by 40% (NEC 220.82(B)), since not all of those loads run at once

Step 6: Add heating or cooling at 100%: Heating and air conditioning sit outside the 40% bucket. NEC 220.82(C) takes the larger of the two at full nameplate value, because whichever one the weather calls for runs continuously while the rest of the house is also drawing power. Folding HVAC into the 40% is the single most common way a DIY panel calculation comes out low.

Step 7: Add EV charging at 100%: NEC 220.57 counts electric vehicle supply equipment at 7,200W or its nameplate rating, whichever is larger, also outside the 40%. Separately, the branch circuit feeding the charger is sized at 125% of its rating because charging is a continuous load: a 48A charger needs a 60A circuit.

Step 8: Convert to amps: Total Amps = Total Watts ÷ 240V

Panel sizing guide:

Signs your panel is overloaded:

• Breakers trip frequently
• Lights dim when large appliances start
• Panel feels warm to touch
• Breakers that won’t reset
• Buzzing or burning smell near the panel (emergency: call electrician immediately)

Planning for future loads:

Leave 20–25% headroom in your panel for future additions. Work out the future load before you add an EV charger, a pool, or a major appliance, not after. A 200A service that lands at 165A today has room for a 32A charger and nothing else.