The answer to 'what size emergency electrical service do I need' is that the size of your emergency electrical service depends on the total electrical load of your home and any critical equipment or appliances you need to power during an outage. Most homes require a 200-amp or 400-amp emergency electrical service to handle the typical electrical load.
The size of your emergency electrical service is determined by a professional electrician who will assess your home's electrical needs and recommend the appropriate service size. They will consider factors like the size of your home, the number and type of electrical devices and appliances you have, and any special power requirements for critical equipment like medical devices, sump pumps, or backup generators.