Well the NEC still uses wattages from old incandescent bulbs for general lighting load calcs, plus there’s always a reasonable amount of overspeccing built into the calculation.

You would then add any large loads specifically. Clothes drier, oven, fridge, HVAC, anything that comes with a wattage rating should be included in the load calc.

Most utilities these days will also just round up to a 200A service for anything larger than a trailer. Big houses would get multiples of 200A services if needed.