To size a generator for an RV, total the appliances that must run together, divide that running load by the calculator’s 0.80 planning factor, and check motor-starting demand separately. Choose a generator whose continuous rating meets the planned running figure and whose starting or surge rating meets the starting-capability figure. Then verify that its voltage, output arrangement, and connection are suitable for the RV; the wattage result alone does not establish compatibility.
How the RV sizing checks work
The method uses two capacity checks because an RV’s steady demand and its brief motor-starting demand are different.
- List the loads that must run together. Include essential loads and any optional appliances you expect to operate at the same time. An appliance you are willing to use only while the air conditioner is off does not have to be part of that simultaneous group.
- Find the simultaneous running load. Running watts describe the power being used while equipment operates normally.
- Allow the calculator’s planning headroom. For these presets, we divide the running load by 0.80. This is a planning policy used by the calculator, not a universal electrical rule for every generator.
- Check starting capability separately. An air-conditioner compressor can require more power while starting than while running. The supplied presets assume one motor starts at a time, so their results do not cover two compressors or other motors starting simultaneously.
- Require both ratings to pass. The generator’s continuous output must meet the planned running-capacity result, while its applicable surge or starting output must meet the starting-capability result. Do not select a generator by comparing only one of those numbers.
For the limited service check on this page, 30 A RV service is treated as one 120 V leg with 3,600 W of nominal capacity. That comparison covers running watts only. It does not verify current, power factor, breakers, wiring, plugs, adapters, or installation suitability.
Worked RV generator-sizing examples
These calculator presets show how air conditioning changes the result. They are reference setups, not measurements of your RV.
| Reference preset | Simultaneous running load | Running capacity to plan for | Required starting capability | Decisive constraint in the preset |
|---|---|---|---|---|
| RV essentials, no rooftop AC | 977 W | 1,222 W | 977 W | Planned running capacity |
| 30 A RV with 13,500 BTU AC | 2,727 W | 3,409 W | 3,952 W | Starting capability |
| 30 A RV with 15,000 BTU AC | 2,913 W | 3,642 W | 4,627 W | Starting capability |
| 50 A RV with two 15,000 BTU AC units | 4,849 W | 6,062 W | 6,563 W | Starting capability, plus an unresolved leg-balance check |
For example, the 30 A preset with a 13,500 BTU air conditioner has a running load of 2,727 W. Dividing that load by the preset’s 0.80 planning factor produces 3,409 W of planned continuous capacity, while the modeled start requires 3,952 W. Starting capability is the higher requirement in this setup, but the generator’s continuous rating still has to meet the planned running figure.
The 50 A dual-AC preset changes the answer because it has a larger simultaneous load and two air conditioners. It reports 6,062 W of planned running capacity and 6,563 W of starting capability under the one-motor-at-a-time assumption. However, total wattage cannot establish 50 A service suitability: a 50 A RV distributes loads across two 120 V legs, and this calculation does not check that distribution. Its service result is therefore unknown—not passed, failed, or zero.
Common sizing mistakes to avoid
Treating running and starting watts as one rating
They are separate checks. Continuous output supports the ongoing load; starting or surge output supports the modeled motor-start event. A generator must satisfy both requirements under the manufacturer’s rating conditions.
Counting every appliance as simultaneous
Separate essential loads from optional ones. If you can turn off the air conditioner before using another high-power appliance, that schedule may lower the simultaneous running load. Enter the revised schedule in the calculator rather than estimating the new result.
Confusing watts with trip energy
Watts measure power at a point in time. Watt-hours and kilowatt-hours measure energy over time. These sizing results do not calculate daily energy, battery runtime, generator runtime, or fuel consumption.
Treating 30 A or 50 A service as a generator size
An RV service label describes the RV’s electrical service, not the complete specification of a suitable generator. The nominal service assessment here is only a running-watts comparison. It is not a guarantee for breakers, wiring, plugs, adapters, or safe installation. For a 50 A RV, total watts also cannot replace checking how loads are divided between the two 120 V legs.
Replacing an unknown rating with zero
If an appliance rating is unavailable, mark it as unknown and look for its nameplate, manual, or model-specific documentation. Leaving it out would understate the load.
Assuming a soft starter guarantees a smaller generator
A soft starter may affect compressor starting behavior, but these results do not calculate a reduced starting requirement. Check the air-conditioner and soft-start manufacturers’ applicable guidance, and do not reduce the supplied starting figure without model-specific, engine-supported data.
Use your RV’s loads for the final check
- Identify each appliance you expect to use. Look for a nameplate, data label, manual, or model-specific documentation. Record running watts and starting watts when both are given. If a value remains unknown, do not enter it as zero.
- Separate essential and optional loads. Decide what must stay on and what can take turns. For example, create one group for normal operation and another for a scheduled high-power appliance used while the air conditioner is off.
- Confirm the air-conditioner rating. If a model-specific value is unavailable, the RV air-conditioner lookup provides planning figures and ranges. A 13,500 BTU unit is listed at 1,750 W (range 1,500–2,000 W) running and 2,975 W (range 2,800–3,500 W) starting. A 15,000 BTU unit is listed at 1,936 W (range 1,690–2,500 W) running and 3,650 W (range 3,300–4,500 W) starting. These are planning values, not specifications for an unidentified unit.
- Enter your loads in the RV Generator Size Calculator. Use your actual appliance group rather than selecting a preset as though it described your RV exactly.
- Compare the correct generator ratings. Check continuous output against planned running capacity and starting or surge output against starting capability. Also verify voltage, output arrangement, connector compatibility, and any 50 A leg-distribution requirement using applicable equipment documentation.
The calculator completes the power estimate, but it does not certify breakers, wiring, adapters, connectors, or an installation.
Calculate your RV’s requirement
Use the RV Generator Size Calculator with the loads that must run together. If you need a planning value for a rooftop unit before entering your loads, review RV air-conditioner running and starting watts.