When selecting a generator for an RV, it is essential to size it according to the highest load, typically the air conditioner. Standard guidelines suggest a minimum of 3,000-3,500W for 30A RVs and 4,500W or more for 50A models, taking into account both running and starting watts.
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Generator sizing and load verification usually requires these tools.
| Tool | Why You Need It |
|---|---|
| 🔧 Best Multimeter for RV | Verify voltage under load |
| 🔧 Best RV Generators | Compare models for your AC size |
| 🔧 Best RV EMS Systems | Monitor voltage when running on generator |
← Electrical Systems · Generator Sizing
Size your generator to your heaviest load—usually the AC. A 13,500 BTU AC needs 1,500–2,000W running and 2,500–3,500W at startup. For 30A rigs with one AC, plan at least 3,000–3,500W. For 50A or dual AC, 4,500W or more. Add a soft-start kit to run AC on smaller generators.
Choosing the right generator size for your RV comes down to one question: how much power do your appliances actually draw? Too small and you can't run what you need. Too large and you pay for watts you'll never use—plus extra weight, noise, and fuel cost.
This guide walks through what determines generator size, the difference between running and starting watts, and how 30A vs 50A rigs change the math. Use our watts, amps & Ohms calculator to verify load and generator sizing. For 15,000 BTU AC specifically, see our best generator for 15,000 BTU RV AC comparison. For how generators fit into your overall setup—converters, inverters, shore power—read our RV electrical systems guide.
The transfer switch automatically selects shore power or generator. Use an EMS or surge protector between generator and RV. A soft-start kit lets smaller generators run AC. Compare models: Best RV Generators. For campground voltage and complete electrical system context, see our authority guides. If your AC is not cooling on generator, sizing and voltage matter. Informational tone—no aggressive CTAs.
Generator size is measured in watts. Your RV's appliances each draw a certain number of watts when running—and some need a surge of power when they first start. Add up the watts of everything you plan to run at once, then add headroom for startup surges. That number is your minimum generator size.
Typical draws: fridge (100–200W), lights (10–50W each), TV (50–150W), microwave (600–1,200W), AC (1,500–3,500W). The AC is usually the biggest consumer and the one that drives generator size for most RV owners. See how many amps RV AC uses for running vs startup draw by unit size.
Running watts are what an appliance needs to stay on. Starting watts (or surge watts) are the brief spike when motors kick on—an AC compressor, for example, can draw 2–3x its running watts for a few seconds at startup.
Generators are rated for both. A 3,500W generator might have 3,500W running and 4,500W surge. You must size for the surge if you run an AC, otherwise the generator can trip or fail to start the unit. Repeated failed startups—where the compressor tries to spin up but the generator sags—are one of the leading causes of premature compressor failure in boondocking setups.
A 30A RV system delivers about 3,600W at 120V. A 50A system provides two legs of 120V (often 50A each), so total available power is much higher—up to 12,000W in theory. In practice, most 50A rigs run multiple ACs and heavy appliances. A 50A RV typically needs a 4,500W–7,000W generator to run one or two ACs plus basics.
For 30A rigs running a single 13,500 BTU AC plus fridge and lights, a 3,000–3,500W generator is usually sufficient. Check your AC's startup amps and compare to the generator's surge rating.
| Appliance | Running Watts | Startup Watts |
|---|---|---|
| 13,500 BTU AC | 1,500–2,000 | 2,500–3,500 |
| 15,000 BTU AC | 2,000–2,500 | 3,500–4,500 |
| Microwave | 600–1,200 | — |
| Residential fridge | 100–200 | 300–600 |
| RV absorption fridge | 150–300 (AC mode) | — |
| Electric water heater | 1,300–1,400 | — |
| TV + laptop | 150–300 | — |
AC startup vs running: The compressor surge is the key. Without soft-start, size for startup watts.
AC units are the main driver of generator size. A 13,500 BTU rooftop AC often draws 1,500–2,000W running and 2,500–3,500W at startup. A 15,000 BTU unit can need 2,000–2,500W running and 3,500–4,500W surge. If your RV AC is running but blowing warm air, follow our complete AC troubleshooting guide. If you're seeing ice buildup on your rooftop unit, read why RV AC units freeze up.
If you don't run the AC, a 2,000–2,200W inverter generator can handle fridge, lights, TV, and charging. If you want to run the AC, plan for at least 3,500W—and 4,500W or more if you have a larger AC or want headroom for other loads.
Inverter generators are quieter and produce cleaner power for electronics, but they typically top out around 2,200–4,500W in portable sizes. Conventional generators can deliver more watts for less money but are louder and produce "dirty" power that can harm sensitive devices.
For boondocking with AC, you often need 3,500W+. That pushes you toward larger inverter units or dual-fuel models. If you skip the AC and only need basics, a 2,200W inverter is enough—and much quieter. Adding solar can cut generator runtime—use solar for daytime charging and reserve the generator for AC or heavy evening loads.
Usually no. A 13,500 BTU AC needs 1,500–2,000W running and 2,500–3,500W surge at startup. A 2,000W generator may trip or fail to start the AC. Plan for at least 3,500W for one AC.
Typically 1,500–2,000W running and 2,500–3,500W at startup. Check your AC's nameplate or manual for exact specs.
Yes. A 30A rig delivers about 3,600W. A 3,500W generator can run one AC, fridge, lights, and small loads—assuming the surge rating covers AC startup.
Yes. Output drops at altitude. Oversize by 10–15% when camping above 5,000 feet. Thin air reduces engine efficiency.
Inverters are quieter and produce cleaner power for electronics. Conventional units deliver more watts for less money but are louder. For AC use, many choose inverter for noise; for heavy loads, conventional can be more economical.
Solar can reduce generator runtime. Use solar for daytime charging and basics; reserve the generator for AC or heavy evening loads. Solar + smaller generator is a common boondocking setup.
Size your generator to your heaviest load—usually the AC—and make sure the surge rating covers startup. For 30A rigs with one AC, 3,000–3,500W is typical. For 50A rigs or dual-AC setups, 4,500W or more is safer.
CTA → Generator Recommendations
Compare models: Best RV Generators. Pair with soft-start to run AC on smaller units. Use an EMS or surge protector at the pedestal. See safe campground voltage.
If you're diagnosing RV electrical or appliance problems, these guides may help:
RV Breaker Keeps Tripping | RV Generator Won't Start | RV Shore Power Not Working | RV Converter Not Charging | RV Inverter Troubleshooting | RV Outlets Not Working | RV Microwave Not Working | RV Refrigerator Not Cooling | How To Test RV Outlet | Best RV EMS
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Last updated: March 2026 · Reviewed for technical accuracy