What size generator do I need for an RV?
A 30 amp RV service is 30 amps at 120 volts, which is 3,600 watts for the whole coach. A 50 amp service is 50 amps at 120/240 volts, which is 12,000 watts total, 6,000 watts per leg. Those are ceilings, not demand: your RV only draws what you switch on.
For boondocking the answer is usually about one appliance, the rooftop air conditioner. A 13,500 BTU unit draws 1,650 watts running (1,900 in desert heat) and its label lists 63 locked rotor amps. With a soft start, a 2,900 watt inverter generator carries one air conditioner on its own, and about 3,500 watts carries it plus lights, a TV, and chargers. Without a soft start, plan on 4,000 watts or more, because the startup surge is what the generator has to survive.
How many watts does a 30 amp RV outlet give you?
A 30 amp RV pedestal or cord is a single 120 volt circuit at 30 amps. Multiply the two: 3,600 watts, and that is the whole budget for the coach. The outlet on the other end is a NEMA TT-30R, rated 30 amps at 125 volts, 2 pole 3 wire. It is a 120 volt outlet with no second hot leg.
That last part matters more than the wattage. A 30 amp RV inlet is not the same thing as a 30 amp dryer or welder outlet, which are 240 volt circuits with a different plug. The adapters sold to bridge the two put 240 volts into a coach wired for 120, which is how converters, televisions, and air conditioners get destroyed. If your RV has a 30 amp cord, it wants 120 volts, 30 amps, and nothing else.
| On a 30 amp (3,600 W) budget | Running watts | Fits? |
|---|---|---|
| One 13,500 BTU A/C, soft start, lights, TV, chargers | 2,085 W | Yes |
| Same, plus the microwave | 3,335 W | Yes, tight |
| Same, plus microwave and coffee maker | 4,235 W | No |
| Two 13,500 BTU A/Cs, lights, TV, chargers | 3,735 W | No |
Running watts only, before any startup surge. Anything in the "tight" row works until the compressor restarts while the microwave is on.
Does a 50 amp RV need a 12,000 watt generator?
No, and this is the most expensive misunderstanding on the subject. A 50 amp inlet is a NEMA 14-50R, 50 amps at 125/250 volts, and 12,000 watts is what it can pass, not what your coach pulls. A 50 amp RV with one air conditioner, a TV, and a laptop draws about 2,000 watts. The 50 amp inlet is bought so you can run both air conditioners, the water heater, and the microwave at once, not because the wiring demands it.
So a 50 amp coach can run off a smaller generator. What you cannot do is run two air conditioners plus the usual loads on a 30 amp generator outlet, because 30 amps is 3,600 watts no matter what is plugged into it.
How many watts does an RV air conditioner use?
The numbers below are from Airxcel's own literature for the Coleman-Mach 3 PLUS 48203, a 13,500 BTU rooftop unit. They are the manufacturer's test-condition figures, not a guess at a typical unit:
13,500 BTU rooftop A/C
- Running watts, ARI condition
- 1,650 W
- Running watts, desert condition
- 1,900 W
- Full-load amps
- 15.3 A
- Locked rotor amps (label)
- 63 A
- Locked rotor at 115 V
- 7,245 W
What soft start does to it
- Start current reduction
- 50 to 70%
- Start current after soft start
- under 20 A
- Watts at 20 A, 120 V
- 2,400 W
- Running with basics
- 2,085 W
- Generator class
- 2,900 W or more
The gap between 1,650 watts running and 63 locked rotor amps is the whole problem. Locked rotor amps are the worst case, the current a motor draws if the rotor cannot turn at all, and the unit ships with a start capacitor and PTCR kit precisely to keep the real startup below that ceiling. The practical sizing rule this site uses elsewhere, two to three times running watts for a motor, puts startup draw at 3,300 to 4,950 watts. Micro-Air, which makes the EasyStart soft start, publishes a 50 to 70 percent cut in start current and states that an RV rooftop compressor equipped with one starts on under 20 amps. That is the difference between a 2,200 watt inverter generator working and tripping its breaker.
Which generator size for which setup?
Every row uses the same arithmetic as the rest of this site: total running watts, plus the surge of the largest single motor, plus a 20 percent buffer, rounded up. Loads that are not the air conditioner come from the appliance wattage chart: TV 110 W, laptop 70 W, 20 LED bulbs 180 W, phone chargers 75 W, microwave 1,250 W, coffee maker 900 W. The four "basics" together add 435 running watts.
| Setup | Running | Peak | Recommended sizeSize | What to look forLook for |
|---|---|---|---|---|
| A/C with soft start, alone | 1,650 W | 2,400 W | 2,900 W | Inverter unit with a TT-30R |
| A/C with soft start, plus basics | 2,085 W | 2,835 W | 3,500 W | 3,500 W with TT-30R |
| A/C, no soft start, alone | 1,650 W | 3,300 W | 4,000 W | 4,000 W with TT-30R |
| A/C, no soft start, plus basics | 2,085 W | 3,735 W | 4,500 W | 4,500 W or larger |
| A/C with soft start, basics, microwave, coffee | 4,235 W | 4,985 W | 6,000 W | 6,000 W and a 50 amp inlet: 4,235 W will not pass a 30 amp cord |
| Two A/Cs with soft start, plus basics | 3,735 W | 4,485 W | 5,400 W | Needs a 50 amp inlet and outlet |
Peak is running watts plus the largest single surge, not the sum of every surge, because the motors do not all start in the same instant. The generator's continuous rating has to cover the running figure; its peak rating has to cover the peak figure.
Which outlet does the generator need?
Watts are only half the purchase. The outlet on the generator decides whether the coach can use them.
- TT-30R (30 A, 120 V) is the outlet a 30 amp RV cord plugs into directly. Some portables label it an "RV outlet". If the generator has one, you are done.
- L5-30R (30 A, 120 V, locking) is also 120 volts and works through a locking-to-TT-30 adapter. Same 3,600 watts.
- L14-30R (30 A, 240 V) is the outlet home backup uses. Through an adapter to a 30 amp RV inlet it delivers one hot leg and the neutral, so the RV still sees 120 volts and is still capped at 30 amps. The generator's 240 volt rating is irrelevant to the coach.
- 14-50R (50 A, 120/240 V) is what a 50 amp RV cord plugs into directly, and what makes two air conditioners possible.
A generator that advertises 7,500 watts through a 240 volt 30 amp outlet cannot give a 30 amp RV more than 3,600 of them. Match the outlet to the cord before you compare wattage numbers.
How is this calculated?
Two rules decide everything on this page, the same two the calculator uses:
- Total running watts must stay under the generator's continuous rating.
- Total running watts plus the single largest surge must stay under the generator's peak rating.
Then a 20 percent buffer, so the generator is not running flat out, and the result is rounded up to the next 100 watts. The 30 and 50 amp service figures are just volts times amps: 30 times 120 is 3,600, and 50 times 240 is 12,000, split as 6,000 watts on each 120 volt leg.
Air conditioner figures are Airxcel's published test-condition numbers for one 13,500 BTU model. Your unit will differ by make, age, and how hot it is outside. The nameplate on the unit is always the better number.
What else should you know before you buy?
- A generator loses capacity in heat and at altitude. Airxcel says so in its own sizing notes: output drops as temperature and elevation rise, which is exactly when you want the air conditioner. If you camp high or in the desert, size up rather than assuming the label figure holds.
- Never backfeed an RV panel or a house panel. A cord with two male ends, or a suicide cord, can kill a lineman and will not be covered by anything. Use the RV's own inlet, and have an electrician fit a proper inlet or transfer switch at home.
- Run the generator outside, away from the coach. Carbon monoxide kills campers every year, and an open window or a nearby exhaust is not protection. Never in a storage bay, never under an awning with the exhaust pointed at the rig.
- Turn big loads off before the compressor starts. The air conditioner restarting while the microwave runs is what trips a 30 amp breaker. Sequencing costs nothing.
- An inverter generator is quieter and safer for electronics. Clean sine wave output matters for laptops, phones, and the converter. If the coach has a converter and you leave it on, its draw is part of your running total.
Add up your own RV loads
Pick the appliances you travel with and get your exact size, with the math shown.
Open the Generator Size Calculator →Where these numbers come from
- Airxcel / Coleman-Mach 3 PLUS 48203 product literature: 13,500 BTU nominal capacity, 1,650 running watts at the ARI condition, 1,900 at the desert condition, 15.3 full-load amps, 63.0 locked rotor amps, 115 V single phase.
- Micro-Air: what EasyStart does and how it works: a 50 to 70 percent reduction in peak start current, and an RV rooftop compressor starting on under 20 amps.
- Leviton 7313: NEMA TT-30R, 30 amp, 125 volt, 2 pole 3 wire, for recreational vehicles.
- Leviton 279: NEMA 14-50R, 50 amp, 125/250 volt.
- TV, laptop, LED bulb, charger, microwave, and coffee maker wattages come from this site's appliance wattage chart, so the rows above agree with the calculator.
Frequently asked questions
What size generator do I need to run one RV air conditioner?
With a soft start installed, a 2,200 to 2,900 watt inverter generator will start and run one 13,500 BTU rooftop air conditioner. Without a soft start, budget 4,000 watts or more, because the compressor's startup surge is what the generator has to survive, not its 1,650 watt running draw.
Can I run my RV air conditioner on a 2,000 watt generator?
Only with a soft start. Without one, a 13,500 BTU rooftop unit's label lists 63 locked rotor amps against 15.3 full-load amps, roughly four times its running current for a fraction of a second, which is more than a 2,000 watt unit's peak rating. Micro-Air, which makes the EasyStart soft start, states that an RV rooftop compressor with their unit can start on under 20 amps, which is about 2,400 watts.
Will a 30 amp generator run a 50 amp RV?
It will run the loads you keep under 3,600 watts, which is all a 30 amp circuit can deliver. The 50 amp inlet is a capacity rating, not a demand: your RV only draws what you switch on. What you cannot do is run two air conditioners plus the usual loads on 30 amps.
What is the difference between a TT-30R and an L14-30R outlet?
A TT-30R is 30 amps at 125 volts, 120 volts only, and it is the outlet an RV's 30 amp cord expects. An L14-30R is 30 amps at 125/250 volts, a four wire 240 volt outlet used for home backup. Fed through an adapter to a 30 amp RV inlet, the RV still gets 120 volts and is still limited to 30 amps, so 3,600 watts.
Do I need a soft start for my RV air conditioner?
You need one if you want to run the air conditioner from a small inverter generator or from a 30 amp pedestal alongside other loads. Micro-Air publishes a 50 to 70 percent reduction in start current, which is the difference between a generator that trips on startup and one that carries the load.
How many watts does a 30 amp RV use?
A 30 amp RV service is 30 amps at 120 volts, which is 3,600 watts for the whole coach. That is a ceiling, not a typical draw. One 13,500 BTU air conditioner plus lights, a TV, and chargers sits around 2,085 watts, which leaves headroom until the microwave or the coffee maker comes on.
Related
- Generator size calculator (add up your own appliances)
- What will a 7,500 watt generator run? (a full worked example)
- What size generator for a fridge and freezer? (RV fridges behave differently)
- Fuel and runtime estimator (how long a tank lasts)
- Portable vs standby generator (which type fits your situation)
Last reviewed November 2026. Appliance wattages are typical values and may differ from your specific models.