Electrical Load Calculator

How It Works

The NEC Article 220 Standard Calculation method determines the minimum electrical service size for a home. It applies demand factors to general lighting and small appliance loads (first 10,000 VA at 100%, remainder at 40%) and uses the larger of heating or AC loads, not both.

The Formula

Variables

• General Lighting — Square footage x 3 VA per sq ft
• Small Appliance — Number of circuits x 1,500 VA each (NEC minimum 2)
• Laundry — 1,500 VA if laundry circuit present
• Demand Factor — First 10,000 VA at 100%, remainder at 40%
• HVAC — Larger of AC or electric heat (they do not run simultaneously)

Example

A 2,000 sq ft home: General lighting = 6,000 VA. 2 small appliance circuits = 3,000 VA. Laundry = 1,500 VA. Total = 10,500 VA. Demand = 10,000 + (500 x 0.4) = 10,200 VA. Add range (8,000), dryer (5,000), water heater (4,500), AC (5,000) = 32,700 VA / 240V = 136A. Use 150A panel.

Tips

• NEC requires a minimum of two 20A small appliance circuits in the kitchen.
• AC and electric heat are not added together -- the NEC uses whichever is larger.
• A standard electric range up to 12 kW is rated at 8 kW demand per NEC Table 220.55.
• If your calculated load is close to 100A, strongly consider upgrading to 200A for future needs.
• Always have a licensed electrician verify load calculations before upgrading your service.