Check the appliances you want to keep running during an outage. You get total running watts, the peak (surge) watts, and a recommended generator size, with the math shown.
Check the appliances you want to run on backup power.
Every appliance has two numbers that matter. Running watts (sometimes called continuous watts) is what it draws steadily once it is on. Starting watts, or surge watts, is the brief spike a motor pulls when it first kicks on. A fridge or a pump can spike to two or three times its running draw for a second or two, then settle back down. Resistive loads like lights, a space heater, or a microwave have no real surge, so their starting and running numbers match.
In normal use your motors do not all start at the exact same instant. The realistic worst case is everything running steadily while your single largest motor starts up. So peak load is the sum of all running watts plus the one biggest starting surge, not the sum of every surge added together. Adding all surges would size you far larger than you need and cost you money on a generator you will never fully load.
Pick a generator rated at or above your peak watts, then leave headroom. Running a generator near its limit all night is hard on it and on your appliances, and it leaves nothing for the next item you decide to plug in. Choosing the next standard size up gives you that cushion. For whole-home backup or many large motors, a permanently installed standby unit and an electrician are the right call.