Home Electrical Panel Load Capacity Calculator
Calculate your home electrical panel's total load capacity, current connected load, and available headroom. Determine whether your panel can safely handle additional appliances or if an upgrade is needed.
Connected Loads
Enter the wattage of your major appliances and systems. Leave blank or 0 if not applicable.
Demand Factor Settings
Formulas Used
1. Panel Total Capacity:
Pcapacity = V × Ipanel
e.g., 200A × 240V = 48,000W
2. NEC 80% Continuous Load Rule (NEC 210.20 / 230.42):
Psafe = Pcapacity × 0.80
Panels must not be continuously loaded beyond 80% of rated capacity.
3. Demand Factor Method:
Pdemand = Ptotal connected × Demand Factor
Not all loads run simultaneously; demand factors account for diversity.
4. NEC 220.83 Optional Calculation (Existing Dwellings):
PNEC = 8,000W + (Ptotal − 8,000W) × 0.40 (when Ptotal > 8,000W)
First 8,000W at 100%, remainder at 40% demand factor.
5. Load Current:
Iload = Pdemand / V
6. Available Headroom:
Headroom (W) = Psafe − Pdemand
Headroom (A) = (Ipanel × 0.80) − Iload
Assumptions & References
- Calculations assume unity power factor (resistive loads). Motor loads (HVAC, pumps) may have lower power factors, increasing actual current draw.
- NEC 210.20(A): Branch circuit conductors and overcurrent devices must be rated at 125% of continuous loads.
- NEC 220.83: Optional method for calculating loads in existing dwelling units — first 8,000W at 100%, remainder at 40%.
- NEC 230.42: Service entrance conductors must be sized for the calculated load.
- The 80% rule applies to continuous loads (operating 3+ hours). Intermittent loads may use 100% of breaker rating.
- Wattage values shown are typical running watts, not startup/surge watts. Motor loads can draw 3–7× running watts at startup.
- This calculator is for estimation purposes only. Always consult a licensed electrician and obtain proper permits for panel work.
- Reference: NFPA 70 National Electrical Code (NEC), 2023 Edition.