RV Generator Size Calculator

Last updated: September 3, 2026

Quick answer Running a 13,500 BTU air conditioner alone takes a 3,000 W minimum, 3,500 W recommended generator (≈1,500 W running + up to ≈2,800 W to start the compressor). With a soft starter, ≈2,000–2,300 W can work.

Your loads (click to toggle; numbers are editable)

Generator targets
Select your loads

How this calculator works

Two numbers decide generator size:

  • Running watts — the sum of everything on at the same time. The target is this sum plus your chosen headroom (generators lose capacity in heat and at altitude, and you don't want to run one pinned at 100%).
  • Starting watts — the running sum plus the single largest start surge (usually the air conditioner). The generator must survive this spike, so it sets the floor when a compressor is on the list.

If a soft starter is selected, the largest AC surge is cut by ~65% — the reduction Micro-Air publishes for EasyStart (60–70%). Everything else stays the same.

Where the numbers come from

Air-conditioner figures follow manufacturer guidance: Micro-Air states a 13,500 BTU unit needs ≈1,500 W running and up to ≈2,800 W starting (Micro-Air generator guide); 15,000 BTU units run ≈1,500–2,000 W with ≈3,000–3,600 W surges per industry charts. Every other preset is a typical nameplate value — your specific model may differ, so check the label. See the full RV appliance wattage chart.

Generator classes this maps to

Target wattsTypical classWhat it means
≤ 2,300 WSmall inverter (2,000–2,300 W)Fridge, lights, electronics; AC only with a soft starter and careful load discipline
3,000–3,600 WMid inverter / small conventionalOne 13.5k BTU AC plus basic loads — the classic RV air-conditioning floor
4,500–5,500 WLarger inverter / conventional15k BTU AC + microwave + comforts without load juggling
≥ 7,000 WLarge / onboard gensetTwo ACs or big residential fridges; also the class of built-in RV generators (2,500–12,500 W per Cummins' sizing chart)

Also check the service side: a 30 A pedestal supplies 3,600 W total and a 50 A supply is two legs × 50 A = 12,000 W — see 30A vs 50A watts.

Frequently asked questions

What size generator runs a 13,500 BTU RV air conditioner?
A 13,500 BTU unit typically draws ~1,300–1,800 W running and up to ~2,800 W for the first second when the compressor starts, so plan for at least a 3,000 W generator — 3,500 W+ is more comfortable once other loads are running. With a soft starter like Micro-Air EasyStart, the start surge drops 60–70% and a 2,000–2,300 W inverter generator can often do it.
Why does starting wattage matter more than running wattage?
Compressors and motors draw several times their running power for a fraction of a second as they start. A generator that cannot supply that brief surge will stall or trip its overload — even though its running rating looks sufficient.
How is this different from brand generator selectors?
Brand selectors steer you toward that brand's models from generic scenario buttons. This calculator starts from the appliances you actually own, shows the running/starting math, and recommends a wattage class — no products attached.

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