RV amp calculator (30 amp vs 50 amp)
Find out whether the air conditioner, microwave, and coffee maker can run together on your hookup, and what size generator you need when there is no pedestal.
| On | Load | Watts |
|---|---|---|
| Roof air conditioner (13,500 BTU) starts near 3,500 W | ||
| Second roof air conditioner starts near 3,500 W | ||
| RV refrigerator on electric starts near 1,000 W | ||
| Microwave | ||
| Converter / battery charger | ||
| Water heater electric element | ||
| Coffee maker | ||
| Hair dryer | ||
| TV and streaming box | ||
| Portable space heater | ||
| LED lights and fans |
Result
Total running load
3,250 W
That is about 27.1 amps at 120 V.
Your 30-amp service can carry about 3,600 W. You are using 90%. That is tight; avoid starting the AC while the microwave runs.
Generator to feed this: at least 4,063 running watts (with 20% headroom) and a starting rating of at least 4,750 W.
Math: amps = watts ÷ 120. A 30-amp RV plug is 120 V × 30 A = 3,600 W. A 50-amp plug has two 120 V legs of 50 A, 12,000 W in total.
30-amp vs 50-amp in plain numbers
A 30-amp RV service uses a three-prong TT-30 plug. It is a single 120-volt circuit, so its capacity is 120 volts × 30 amps = 3,600 watts. A 50-amp RV service uses a four-prong 14-50 plug with two separate 120-volt “legs,” each good for 50 amps. That is 2 × 120 × 50 = 12,000 watts, more than three times a 30-amp rig. The difference is why a 50-amp coach can run two air conditioners and a 30-amp trailer usually cannot.
Amps are just watts divided by volts. An RV air conditioner drawing 2,000 running watts uses about 16.7 amps at 120 V, more than half of a 30-amp service before anything else is on. Add a 1,200-watt microwave (10 amps) and a converter charging the batteries, and you are at the breaker limit.
Why the air conditioner decides everything
The rooftop AC is usually the largest load and the only big motor. Its compressor needs a starting surge well above its running draw, which is why a small inverter generator may run the AC once it is going but stall when the compressor starts. The calculator adds the AC’s extra starting watts to your total to give the starting rating your generator needs. Many owners fit a soft-start device to the AC to lower that surge; if you have one, lower the starting figure to match the maker’s spec.
Using the result with a generator
When you run from a generator instead of a pedestal, the generator must cover both numbers: the running total (with headroom, so it is not run flat out) and the peak when the AC starts. Two small inverter generators linked in parallel are a common way to reach the power needed for a 30-amp rig with an AC while keeping each unit light. Check that the generator has the right outlet (TT-30R for 30-amp; a 14-50R for 50-amp) or use a properly rated adapter.
Wattages vary by model. Your AC, fridge, and converter nameplates or manuals are the real numbers; edit the table to match. For household sizing, use the generator size calculator, and see our guide to sizing a generator for an RV.