Pick what you want to run at the same time and this recommends an inverter size, accounting for the startup surge that trips undersized inverters.
Buy pure sine wave for anything with electronics. And remember the batteries have to keep up: a 2000W load pulls roughly 170 amps from a 12V bank.
How it works: recommended size = your simultaneous running watts plus 20% headroom, or running watts plus the single biggest startup surge, whichever is larger.