Electrical Panel Load Calculator Formula
Understand the math behind the electrical panel load calculator. Each variable explained with a worked example.
Formulas Used
Total Connected Load
total_watts = total_loadTotal Amperage
total_amps = panel_voltage > 0 ? total_load / panel_voltage : 0Minimum Panel Size
panel_size = panel_voltage > 0 ? ceil(total_load / panel_voltage / 25) * 25 : 0Variables
| Variable | Description | Default |
|---|---|---|
general_lighting | General Lighting & Receptacles(W) | 4800 |
kitchen_circuits | Kitchen Small-Appliance Circuits(W) | 3000 |
laundry_circuit | Laundry Circuit(W) | 1500 |
hvac_load | HVAC (Heating or Cooling)(W) | 5000 |
water_heater | Water Heater(W) | 4500 |
other_loads | Other Fixed Loads(W) | 2000 |
panel_voltage | Panel Voltage(V) | 240 |
total_load | Derived value= general_lighting + kitchen_circuits + laundry_circuit + hvac_load + water_heater + other_loads | calculated |
How It Works
Panel Load Calculation
Add all branch circuit loads in watts. Divide by the panel voltage to get total amperage. Compare against the panel main breaker rating. Standard residential panels are 100A, 150A, or 200A at 240V.
Total Amps = Total Watts / Voltage
Worked Example
Typical home: 4800W lighting, 3000W kitchen, 1500W laundry, 5000W HVAC, 4500W water heater, 2000W other.
- 01Total = 4800 + 3000 + 1500 + 5000 + 4500 + 2000 = 20,800W
- 02Amps = 20,800 / 240 = 86.7A
- 03Minimum panel = 100A (round up to next standard)
Frequently Asked Questions
Does this include NEC demand factors?
This is a simplified calculation. The NEC allows demand factors (e.g., first 3000W of general lighting at 100%, remainder at 35%) which can significantly reduce the computed load.
When should I upgrade to a 200A panel?
If your calculated load exceeds 80% of a 100A or 150A panel, or if you plan to add major loads like an EV charger, consider a 200A panel.
Ready to run the numbers?
Open Electrical Panel Load Calculator