Electrical Load Calculator: Size Your Panel and Circuits Correctly

Adding a hot tub, an EV charger, or a new workshop without checking your electrical panel first is a recipe for tripped breakers and potentially a fire hazard. Before calling an electrician (or doing permitted work yourself), understanding your home's total electrical load tells you whether your panel has capacity to spare or is already near its limit.

The CalcHub Electrical Load Calculator calculates total amperage demand and helps you determine if your service panel is sized adequately.

How Electrical Load Is Calculated

Total Load (watts) = Sum of all appliance wattages in use simultaneously Amperage = Watts ÷ Voltage

• 120V circuits: small appliances, outlets, lighting
• 240V circuits: HVAC, electric range, water heater, dryer, EV charger

Service capacity = Panel amperage × 240V A 200A panel provides 200 × 240 = 48,000 watts (48 kW) of theoretical capacity. In practice, the NEC requires that total connected load doesn't exceed 80% of capacity for continuous loads.

Typical Load by Appliance

Appliance	Typical Wattage	Circuit Size
Central AC (3-ton)	3,500W	240V/20A
Electric furnace	10,000–20,000W	240V/60–100A
Electric range/oven	8,000–12,000W	240V/50A
Electric water heater	4,500W	240V/30A
Clothes dryer	5,000–7,000W	240V/30A
EV charger (Level 2)	7,200–9,600W	240V/50–60A
Hot tub	5,000–7,500W	240V/50A
Refrigerator	150–400W	120V/15–20A
Dishwasher	1,200–1,800W	120V/20A
Microwave	900–1,800W	120V/20A
Washer	500W	120V/20A
Lighting (whole house)	1,000–3,000W	Multiple

Standard Demand Load Calculation (NEC Article 220)

The NEC uses a "demand factor" approach — it recognizes that not all loads run simultaneously. The simplified residential calculation:

1. Lighting and small appliances: 3 VA per sqft (NEC 220.12)
2. Kitchen small appliance circuits: 1,500 VA × number of circuits
3. Laundry circuit: 1,500 VA
4. Large appliances: Nameplate rating
5. Apply demand factors to the total

For a 2,000 sqft home:

• Lighting: 2,000 × 3 = 6,000 VA
• Kitchen circuits (2): 3,000 VA
• Laundry: 1,500 VA
• Electric range (8,000 VA): apply 80% demand = 6,400 VA
• AC (3,500 VA): 100%
• Water heater (4,500 VA): 100%
• First 10,000 VA at 100%, remainder at 40%

This gets complicated quickly — that's exactly what the calculator is for.

Panel Size Sufficiency Check

Panel Size	Typical For	EV Charger Feasible?
60A (older homes)	Limited loads, no major electric appliances	No — need upgrade
100A	Smaller homes, gas appliances	Possibly with load management
150A	Average home	Usually yes, with some planning
200A	Most modern homes	Yes — standard recommendation
400A	Large homes, all-electric, multiple EVs	All-electric home with fleet

If you're adding significant loads (EV charger + HVAC upgrade + electric range), a 100A panel is almost certainly inadequate and a 200A service upgrade is likely needed.

What does it cost to upgrade from 100A to 200A service?

Typically $1,500–$4,000 depending on whether the utility needs to upgrade the drop, meter socket, and panel, and how much rewiring is required. In older homes with aluminum wiring, the project can be more complex.

Can I add a sub-panel instead of upgrading the main panel?

Yes — if your main panel has available amperage, adding a sub-panel (for a workshop, garage, or addition) can be more economical than a full service upgrade. A sub-panel needs a dedicated circuit from the main with appropriate wire gauge and breaker size.

What's the 80% rule for circuit breakers?

Circuit breakers should only be loaded to 80% of their rated ampacity for continuous loads (loads lasting 3+ hours). A 20A circuit should carry no more than 16A continuously. This is why most outlets are on 15A or 20A circuits rather than running everything on one large breaker.

Related Tools

• Power Consumption Calculator — detailed appliance energy usage
• LED Resistor Calculator — low-voltage lighting circuit design
• HVAC BTU Calculator — properly sized HVAC to control electrical demand