Electrical Panel Load Calculator
Calculate total electrical panel load from all branch circuits for service sizing. Enter values for instant results with step-by-step formulas.
Formula
Total Demand = Demand(General + Small Appliance) + Range x 0.80 + Dryer + Water Heater + HVAC + Other
General lighting and small appliance loads are combined, with the first 3,000W at 100% and the remainder at 35% per NEC Article 220. Individual appliances are added at their specific demand factors. Total demand in watts divided by service voltage gives the required amperage for service sizing.
Worked Examples
Example 1: Standard 2,000 Sq Ft Home
Problem: Calculate the electrical service size for a 2,000 sq ft home with electric range (8 kW), electric dryer (5 kW), water heater (4.5 kW), and 5 kW central AC.
Solution: General lighting: 2,000 sq ft x 3 W/sqft = 6,000 W\nSmall appliance circuits: 3,000 W\nLaundry circuit: 1,500 W\nGeneral + small + laundry = 10,500 W\nDemand: 3,000 + (10,500 - 3,000) x 0.35 = 3,000 + 2,625 = 5,625 W\nRange: 8,000 x 0.80 = 6,400 W\nDryer: 5,000 W (minimum)\nWater heater: 4,500 W\nHVAC: 5,000 W\nTotal demand = 5,625 + 6,400 + 5,000 + 4,500 + 5,000 = 26,525 W\nAmps = 26,525 / 240 = 110.5 A
Result: Total demand: 26,525 W (110.5 A) | Recommended: 125A or 150A service
Example 2: Large Home with EV Charger
Problem: Calculate service size for a 3,500 sq ft home with all electric appliances plus a 48A EV charger (11,520 W).
Solution: General lighting: 3,500 x 3 = 10,500 W\nSmall appliance + laundry = 4,500 W\nGeneral subtotal = 15,000 W\nDemand: 3,000 + 12,000 x 0.35 = 7,200 W\nRange (12 kW): 12,000 x 0.80 = 9,600 W\nDryer: 5,500 W | Water heater: 5,500 W\nHVAC: 7,500 W | EV charger: 11,520 W\nTotal demand = 7,200 + 9,600 + 5,500 + 5,500 + 7,500 + 11,520 = 46,820 W\nAmps = 46,820 / 240 = 195.1 A
Result: Total demand: 46,820 W (195.1 A) | Recommended: 200A service (at 97.5% utilization, consider 225A)
Frequently Asked Questions
How do I calculate the total electrical load for a residential panel?
Residential panel load calculation follows NEC Article 220, which uses a standard calculation method. First, calculate the general lighting load at 3 watts per square foot of living space or use the actual connected lighting load, whichever is larger. Add two small appliance circuits at 1,500 watts each (3,000 total) and one laundry circuit at 1,500 watts. Apply the NEC demand factor: first 3,000 watts at 100 percent, remaining watts at 35 percent. Then add individual appliance loads like the range, dryer, water heater, and HVAC at their specific demand factors. The total gives you the demand load in watts, which divided by service voltage gives you the required amperage.
What size electrical service do I need for my home?
Most modern homes require a 200-amp service panel. A 100-amp service is adequate for small homes under 1,500 square feet without electric heat, electric cooking, or central air conditioning. A 200-amp service handles most homes up to 3,000 square feet with full electric appliances, central HVAC, and moderate additional loads. Homes over 3,000 square feet, homes with electric vehicle chargers, pools, hot tubs, workshops, or multiple HVAC systems may need 300 or 400-amp services. The NEC requires that the calculated demand load not exceed 80 percent of the service rating for continuous loads. Always calculate the actual demand before selecting a service size.
What is the 80 percent rule for electrical panels?
The 80 percent rule stems from NEC Section 210.20, which states that continuous loads (running 3 hours or more) must not exceed 80 percent of the overcurrent device rating. For a 200-amp panel, the maximum continuous load is 160 amps. This derating accounts for heat buildup in breakers during sustained loading, which can cause nuisance tripping or accelerated wear. Non-continuous loads can use the full 100 percent of the panel rating. In practice, most residential loads are a mix of continuous and non-continuous, so electricians use the 80 percent rule as a general guideline. Some breakers are specifically rated for 100 percent continuous loading but cost significantly more.
How do I account for future electrical load growth?
Planning for future load growth is essential to avoid expensive service upgrades later. The NEC recommends designing electrical systems with at least 25 percent spare capacity. Common future loads include electric vehicle chargers (40 to 50 amps each), heat pumps replacing gas furnaces, additional kitchen circuits, home offices, workshops, and pools or hot tubs. An EV charger alone can add 7,200 to 11,500 watts of load. If your current demand calculation shows 150 amps on a 200-amp service, you have only 50 amps of spare capacity, which may not be enough for an EV charger plus other additions. Consider installing a larger service now if future electrification is likely.
Can I add circuits to my existing electrical panel?
You can add circuits only if your panel has available breaker spaces and sufficient capacity. First, perform a load calculation to determine your current demand, then subtract from the panel rating to find spare capacity. If your 200-amp panel has a calculated demand of 165 amps, you have 35 amps of capacity available for new circuits. A 20-amp general purpose circuit adds a maximum of 2,400 watts at 120 volts. A 240-volt EV charger circuit adds 7,680 to 11,520 watts. If adding new loads would exceed the panel capacity, you need a service upgrade. Some utilities also limit the service size available to residential customers based on their transformer and service drop capacity.
What is the difference between a load center and a panelboard?
A load center is the standard residential electrical panel, typically rated up to 200 amps and designed for plug-in circuit breakers. Load centers come in main breaker or main lug configurations and typically have 20 to 42 circuit spaces. A panelboard is the commercial and industrial equivalent, built to higher standards with bolt-on breakers and ratings up to 1,200 amps. Panelboards offer better short-circuit current ratings, more robust bus construction, and compatibility with a wider range of breaker types including molded case circuit breakers. For residential applications up to 200 amps, load centers are standard. For 400-amp residential services, two 200-amp load centers or a commercial panelboard are used.