Enter home square footage, major appliances, and HVAC load — get total connected load, NEC demand load, and a clear answer on whether the existing service is sufficient.
Panel upgrade, service change, and load calculation quote forms — professional, ready to print and hand to the customer.
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NEC Article 220 defines how to calculate residential service load. The process has two parts: connected load (everything that could run at once) and demand load (what NEC allows you to assume will actually run simultaneously, using demand factors). A house's connected load is almost always larger than its demand load — which is why most 200A services work fine even with many circuits.
NEC 220.12 requires 3 VA/sq ft for general lighting. A 2,000 sq ft home starts at 6,000 VA in connected load. Apply the demand factors from Table 220.42 (100% of first 3,000 VA + 35% of the remainder) and the lighting load in demand terms drops to about 2,950 VA. This is how a modern home with dozens of circuits still fits within 200A service.
A 100A, 240V service delivers 24,000 VA of capacity. An older home with electric heat, electric range, and a new EV charger can exceed this — especially at peak. NEC requires the calculated demand load to not exceed 83% of service capacity (leaving a safety margin). If you're adding an EV charger to a fully loaded 100A service, you almost certainly need a 200A upgrade. Use this calculator to show the customer why — in numbers.
EV chargers are the single biggest reason homeowners are upgrading panels in 2025–2026. A 48A Level 2 charger adds 11,520 VA of connected load. When that's the last straw on a 100A or older 150A panel, it's an automatic panel upgrade conversation. Ask about EVs on every service call — it's not upselling, it's future-proofing the customer's home.
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Before adding circuits, upgrading a panel, or quoting a service upgrade, you need to know the building's actual electrical load. This calculator performs a standard load calculation based on square footage, appliances, HVAC, and special loads to determine the minimum service size required. Use it to size panels correctly and avoid calls back to upgrade an undersized service.