Electrical Panel Load Capacity Calculator
Determine your electrical panel's total capacity, current load, available capacity, and whether your panel can handle additional loads — based on NEC (National Electrical Code) guidelines.
Common sizes: 100A, 150A, 200A, 400A
Sum of all breaker amperage currently in use (or leave blank to enter watts)
Total wattage of all connected loads (optional alternative to amps above)
NEC recommends 80% continuous load limit for panel capacity planning
Size of new circuit or appliance you want to add
Formulas Used
Total Panel Capacity (Single Phase):
Ptotal = V × Ipanel
e.g., 240V × 200A = 48,000 W (48 kW)
Total Panel Capacity (Three Phase):
Ptotal = V × Ipanel × √3
e.g., 208V × 200A × 1.732 = 72,070 W (72 kW)
Usable Capacity (NEC 80% Rule):
Iusable = Ipanel × (Demand Factor / 100)
e.g., 200A × 0.80 = 160A usable
Available Capacity:
Iavailable = Iusable − Icurrent load
Load from Watts (Single Phase):
I = P / V
Load from Watts (Three Phase):
I = P / (V × √3)
Load Percentage:
Load% = (Iload / Iusable) × 100
Assumptions & References
- NEC Article 220: Branch-circuit, feeder, and service load calculations.
- NEC 210.20(A): Continuous loads must not exceed 80% of the overcurrent device rating.
- NEC 230.42: Service entrance conductor sizing based on calculated load.
- Power factor is assumed to be 1.0 (unity) for resistive loads. Inductive loads (motors, HVAC) may have PF of 0.8–0.95, increasing actual current draw.
- Three-phase calculations use the line-to-line voltage and the √3 (≈1.732) factor.
- The 80% demand factor is the NEC standard for continuous loads (operating 3+ hours). Non-continuous loads may use 100%.
- This calculator provides estimates for planning purposes only. Always consult a licensed electrician for actual panel work.
- Panel upgrades typically require a permit and inspection by your local Authority Having Jurisdiction (AHJ).