Add up the running watts of everything that will be on at the same time, then the highest startup surge.
Pick an inverter whose continuous rating is at least 125% of your running load and whose surge rating covers the biggest motor start (fridges, AC, pumps and microwaves). The DC current is amps = watts ÷ (battery volts × efficiency); a 2,000 W load on 12 V pulls about 185 A, which is why bigger systems move to 24 V or 48 V.
| Appliance | Running | Startup |
|---|---|---|
| 13,500 BTU RV AC | 1,200–1,500 W | 2,000–3,500 W (less with soft start) |
| Microwave (1,000 W cooking) | 1,400–1,700 W | about the same |
| Residential fridge | 100–250 W | 600–1,200 W |
| Coffee maker | 800–1,200 W | — |
| TV + streaming box | 60–150 W | — |
Safety: These are general estimates, not a design. Follow your equipment manufacturer's instructions and local electrical code, and consult a qualified electrician for anything connected to shore power, a house, or high-current batteries.
At least 125% of the running watts you will use at once, with a surge rating above your biggest motor start. Many RVers pick 2,000 W; 3,000 W if they want to run the AC or a microwave plus other loads.
For RVs, yes in most cases: microwaves, fridges, CPAP machines and electronics run cooler and more reliably on pure sine wave.
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