RV Generator Size Calculator

How RV generator sizing works

The roof air conditioner decides almost everything. A typical 13,500 BTU unit runs at about 1,500 W but pulls around 3,500 W for a second while its compressor starts; a 15,000 BTU unit is closer to 1,800 W running and 4,000 W starting. We add up the running watts of everything on, add the single biggest start-up surge, then compare that with common generator sizes, keeping 20% headroom on running watts.

Your shore power sets a ceiling: a 30 A RV can't use more than 3,600 W (30 A × 120 V) before its main breaker trips, and a 50 A RV gets two 50 A legs, 12,000 W in total. There's no point buying a generator much bigger than your RV can draw.

Will a 2,200 W inverter generator run a 13,500 BTU RV air conditioner?

Usually only with a soft starter and little else running. A typical 13,500 BTU roof AC runs at about 1,500 W but needs around 3,500 W for a second to start. A soft starter cuts that surge by roughly two-thirds, to about 2,200 W, which is at the limit of a 2,200 W inverter. At altitude or in heat, expect it to struggle.

What size generator for a 30 amp RV?

A 30 A RV can draw at most 3,600 W (30 A at 120 V), so a generator rated about 3,000–3,600 W running covers everything the RV can use. Many owners get by with a 3,200 W class inverter or two 2,200 W inverters in parallel.

What size generator for a 50 amp RV?

A 50 A RV service is two 120 V legs of 50 A, up to 12,000 W. Few owners use all of it; size to what you actually run, typically two roof ACs plus kitchen loads, which is often 6,000–8,000 W starting. Two ACs only need one surge allowance if they start one after the other (many RVs have a load manager that staggers them).

Sources: typical RV appliance and roof AC wattages from manufacturer spec sheets and generator worksheets (check your unit's label); soft-start reduction as claimed by soft-starter makers (60–70%); CPSC generator safety guidance.