What size inverter for an RV or camper van

An inverter turns 12 V battery power into 120 V household power. How big it needs to be depends on which 120 V appliances run at the same moment, not on how much energy you use in a day. Get that right and you avoid both a tripping inverter and an oversized one that wastes power and needs huge cables.

Step 1: list only the 120 V AC loads

Plenty of RV and van loads run straight from 12 V and never touch the inverter: compressor fridges, roof fans, LED lights, the water pump, USB phone charging, a Starlink Mini, a diesel heater and the furnace blower. The weekender van preset is all 12 V, so the calculator says no inverter is needed at all.

The loads that need an inverter are things with a household plug: laptop chargers, TVs, a Starlink Standard, a CPAP if you use its 120 V adapter, microwaves, coffee makers, kettles, hair dryers, induction cooktops, a residential fridge and a roof air conditioner. The appliance wattage chart lists typical watts for each.

Step 2: add up what runs at the same time

The calculator adds the watts of every AC load that can run together. Some loads are short and usually run alone, such as a coffee maker, kettle, hair dryer or blender; for those it uses the biggest single one instead. Then it takes the larger of those two numbers, adds 25% headroom, and rounds up to a common inverter size (150, 300, 500, 700, 1,000, 1,200, 1,500, 2,000, 2,500, 3,000 W and up).

AC loads	Peak watts	× 1.25	Inverter size	Surge to cover
32 in TV only	50 W	63 W	150 W	50 W
Laptop charger + TV	115 W	144 W	150 W	115 W
Residential fridge (120 V) only	150 W	188 W	300 W	750 W (start-up)
Coffee maker (one at a time) + laptop + TV	900 W	1,125 W	1,200 W	900 W
Electric kettle only	1,500 W	1,875 W	2,000 W	1,500 W
Class C preset: microwave + laptop + TV (coffee maker on its own)	1,615 W	2,019 W	2,500 W	2,065 W
Full-time van preset: induction cooktop + laptop	1,865 W	2,331 W	2,500 W	1,865 W
Microwave and induction cooktop together	3,300 W	4,125 W	5,000 W	3,750 W

Two lessons stand out. First, one big appliance sets the size: a single 1,500 W kettle needs a 2,000 W inverter even if everything else is tiny. Second, running two big cooking loads at once doubles the inverter. If you can use the microwave and the induction cooktop one at a time, a 2,500 W inverter covers either one; leave them “on together” and the calculator asks for 5,000 W, which is impractical on a 12 V system.

The 25% headroom is deliberately conservative. Plenty of owners run a 1,500 W microwave on a 2,000 W inverter. The headroom covers a small load running alongside the big one, a hot inverter running below its label, and the gap between a nameplate rating and real draw.

Open the Class C preset Coffee maker, laptop and TV Kettle only

Step 3: check start-up surge

Anything with a motor or compressor draws extra power for a moment when it starts. The calculator estimates surge as the running total plus the largest extra start-up draw. The library uses 5× running watts for a residential fridge compressor, 2.5× for a roof air conditioner with a soft starter, 2× for a blender and 1.3× for a microwave.

Many inverters can surge to about twice their rating for a few seconds. A residential fridge alone only needs about 188 W of running capacity, but its start-up can reach about 750 W, more than twice a 300 W inverter, so the calculator warns you. Pick an inverter whose published surge rating covers the number shown. For an air conditioner, see running an RV air conditioner on solar.

Pure sine wave, and the cost of leaving it on

Choose a pure sine wave inverter for RV use. Modified sine wave units are cheaper, but some laptop chargers, CPAP machines, compressor fridges, microwaves and anything with a motor can run hot, buzz or misbehave on them.

An inverter also uses power just by being on. RVWatt assumes 10 W of idle draw for as long as your longest-running AC load is on. With a residential fridge, the inverter stays on 24 hours, which adds 240 Wh a day before the fridge uses anything. That is why the 120 V fridge on its own comes to about 1,640 Wh a day from the battery. A much bigger inverter than you need usually has higher idle draw too, so oversizing has a daily cost, not just a purchase cost.

Battery current, fuse and cable

Inverters pull very high current from a 12 V bank. The calculator works out the DC current at full rated output and at 10.5 V, the typical low-battery cutoff, where current is highest. It assumes 90% inverter efficiency, adds 25% for the fuse, and picks the smallest copper cable that carries the fuse rating (ABYC 90 °C table) with no more than 3% voltage drop. The table uses the calculator’s default 6 ft round trip between battery and inverter.

Inverter	12 V: amps / fuse / cable	24 V: amps / fuse / cable	48 V: amps / fuse / cable
1,000 W	106 A / 150 A / 2 AWG	53 A / 70 A / 8 AWG	26 A / 35 A / 12 AWG
1,500 W	159 A / 200 A / 1 AWG	79 A / 100 A / 6 AWG	40 A / 50 A / 10 AWG
2,000 W	212 A / 300 A / 3/0 AWG	106 A / 150 A / 2 AWG	53 A / 70 A / 8 AWG
2,500 W	265 A / 350 A / 4/0 AWG	132 A / 175 A / 2 AWG	66 A / 90 A / 6 AWG
3,000 W	317 A / 400 A / beyond 4/0 AWG	159 A / 200 A / 1 AWG	79 A / 100 A / 6 AWG

A 3,000 W inverter at 12 V needs a 400 A fuse, which matches what Victron specifies for its MultiPlus-II 12/3000, and more cable than a single 4/0 run carries. That is where 24 V or 48 V starts to make sense. Longer cable runs need thicker cable; enter your own run length in the calculator. Your inverter manual’s fuse and cable requirements always take priority over these starting points.

The battery bank has to supply that current too. The calculator warns when full inverter output would exceed about 1C for LiFePO4 or 0.2C for AGM. A 2,000 W inverter on a single small battery is a common mismatch; see LiFePO4 vs AGM.

Wiring an inverter into the RV

A standalone inverter with its own outlets is the simplest setup. Connecting an inverter or inverter-charger to the RV’s 120 V panel is different: it needs a transfer switch (built in or separate) so shore power, a generator and the inverter can never feed the same circuit at once, and so the inverter never back-feeds the shore cord. That is work for a qualified RV electrician or licensed electrician. Fuse the battery cable close to the battery, use properly crimped lugs and follow the inverter’s grounding instructions.

Size an inverter for your own loads

Frequently asked questions

What size inverter do I need for an RV microwave?

For a typical 1,000 W microwave, which draws about 1,500 W from the outlet, RVWatt suggests a 2,000 W pure sine inverter on its own, or 2,500 W if a laptop and TV may run at the same time, as in the Class C preset. Plenty of owners run a microwave on 2,000 W. At 12 V a 2,000 W inverter can draw about 212 A from the battery at full output, so it needs a 300 A fuse and heavy cable.

Is a 2,000 W inverter enough for a camper?

For most campers, yes, as long as only one big appliance runs at a time. It covers a microwave, a kettle, a hair dryer or a coffee maker, plus small loads. It does not cover a microwave and an induction cooktop together, and a roof air conditioner needs a soft starter and a large lithium bank. If your loads are only a laptop, a TV and phone chargers, a 150 W to 300 W inverter is enough.

Do I need an inverter for a 12 V fridge?

No. A 12 V compressor fridge runs straight from the battery. Only appliances with a household 120 V plug need an inverter. A residential 120 V fridge does need one, and it keeps the inverter on all day, which adds about 240 Wh a day of idle draw at 10 W.

Should I use 12 V or 24 V for a big inverter?

At 2,000 W and up, consider 24 V or 48 V. A 3,000 W inverter draws about 317 A at a low 12 V battery and needs a 400 A fuse and more than a single 4/0 cable. At 24 V it is about 159 A with a 200 A fuse and 1 AWG cable at a short run. The rest of the system has to match the voltage you choose.

Related guides

Safety: high-current DC is dangerous. A 12 V battery bank can deliver thousands of amps into a short circuit, enough to melt tools, weld rings and watches to terminals, ignite insulation and start a vehicle fire in seconds. Lithium and lead-acid batteries can also vent, burn or explode if overcharged, damaged or charged outside their temperature limits. Remove jewelry, use insulated tools, disconnect the battery before working, fuse every positive conductor as close to the battery as practical with a fuse rated for the battery's short-circuit current (often a Class T for lithium banks), use properly crimped lugs and pure copper cable, and secure batteries against movement. If you are not confident, hire a qualified RV or marine electrician. RVWatt provides estimates only; see our Terms of Use.

These figures are planning estimates from typical appliance ratings and NASA monthly sun averages for a flat, horizontal panel. Your real use will differ with heat, shade, dirty panels and how you actually live in the rig. Follow your equipment manuals and have a qualified installer check high-current wiring.