You're sizing a residential service panel and the NEC gives you demand factor tables that nobody actually totals by hand. You check off appliances, guess at square footage loads, and hope the electrician catches the errors. This calculator does the NEC Article 220 demand calculation automatically: pick your appliances and square footage, and it totals the connected load, applies the correct demand factors, and sizes the service. Use it before you spec the panel.
The NEC general lighting load alone — 3 W/SF — eats 6,000 watts on a 2,000 SF house before you plug in a single appliance. Add a range (12,000 W), dryer (5,000 W), AC (4,000 W), and water heater (4,500 W), and you're at 31,500 W. At 240V that's 131 amps — 200-amp service, no question. The 100-amp panel only works for small houses with gas appliances.