What Size Inverter Do I Need for My RV?

For most RVs the answer is 2,000 watts — it runs a microwave or a coffee maker with margin, and it matches what a two-battery lithium bank can actually deliver. Go to 3,000W only if you will run two big loads at once and your bank carries 300A of BMS rating to feed it. Stay at 1,000–1,200W if one 100Ah battery is all the bank you have — because that battery, not the inverter, is your real limit.

That last clause is the part every sizing chart for this query leaves out, and it is where this page starts.

Three numbers, in the right order

The pages ranking for this query hand you a formula — add up your appliance watts and multiply by 1.4 — and stop. That produces an inverter that starts your loads and then discovers, on its first weekend out, that the battery bank disconnects whenever the microwave runs.

Sizing that works needs three numbers, checked in order:

1. Your biggest simultaneous load. Not the sum of every appliance you own — the most you will genuinely run at once. Watts, from the labels.
2. The startup surge of the worst load in that set. Compressors and motors pull far more for a moment than they run at.
3. What your battery bank will pass. The BMS continuous rating, in amps, which caps everything above it no matter what the inverter is rated for.

The first two size the inverter. The third decides whether you are allowed to buy it yet.

Step one: what actually runs at once

Typical draws for the appliances people buy inverters for. These are representative ranges — the number that matters is on your appliance’s own label, so check it before buying anything. To have the peak, the surge and the BMS check done from your own list, the RV battery calculator sizes the inverter and the bank together.

Load	Typical running draw	Startup behaviour
LED lighting, phone charging	5–30W	—
Laptop	60–100W	—
TV	60–150W	—
CPAP (no humidifier)	30–60W	—
Residential 12 cu ft fridge	100–200W	Compressor start, several × running
Coffee maker	900–1,400W	—
Microwave (1,000W cooking power)	1,400–1,600W from the outlet	Brief start spike
Toaster	800–1,500W	—
Induction burner	1,500–1,800W	—
Hair dryer	1,200–1,875W	—
13,500 BTU air conditioner	1,300–1,700W	Large start surge — see below

Two things stand out. Anything with a heating element lives in the 1,000–1,800W band, which is why 2,000W is the workhorse size. And a microwave’s cooking power is not its draw — a “1,000W” microwave takes roughly 1,500W from the outlet, a distinction that has undersized a lot of inverters. Loads with motors or transformers also care what shape of power they get, which is the pure sine question — settle it alongside the wattage.

Step two: the surge, and how long it is allowed to last

Motors and compressors pull two to three times their running draw at startup. Inverters carry a surge rating for exactly this, but the ratings are shorter than the shopping pages imply, and the honest manufacturers publish the window: Renogy’s 4,000W and 6,000W surge figures are for one second; Xantrex publishes 4,000W for five seconds on the Freedom XC 2000; Go Power states no duration at all for the ISW series.

One second starts a fridge compressor. It does not run an air conditioner through a hard start — a 13,500 BTU unit’s compressor is the surge that defeats otherwise sensible systems, which is why the workable answer there is a soft starter plus the 3,000W class, and why most owners simply leave the air conditioner on shore power. The full arithmetic, parts list included, is in running an RV air conditioner on batteries.

Step three: the ceiling your battery sets

This is the number the sizing charts skip. Every lithium battery has a battery management system with a continuous current limit, and when the inverter asks for more, the battery disconnects — instantly and completely, regardless of how full it is. Most 100Ah batteries carry a 100A BMS, which at 12.8V is about 1,280W of sustained output.

The inverter also takes its cut: at Renogy’s published minimum of 85% full-load efficiency, a 2,000W output costs the bank about 2,350W.

1 × 100Ah lithium battery 100A BMS

1,280W

Comfortable with a 1,000W inverter; disconnects under a 2,000W unit at full load.

2 × 100Ah in parallel 200A BMS

2,560W

The 2,000W pairing — the most common correct answer.

3 × 100Ah in parallel 300A BMS

3,840W

What the 3,000W class actually requires.

Battle Born GC3, single battery 300A BMS

3,840W

300A from one case — the single-battery route to 3,000W.

01,0002,0003,0004,000

1,000W inverter draws ~1,180W 2,000W inverter draws ~2,350W 3,000W inverter draws ~3,530W

Read it bottom-up when shopping: find your bank, and buy the largest inverter whose marker sits inside your bar. If the inverter you want sits outside it, the next purchase is a battery, not an inverter — the battery roundup compares the BMS figures directly, and what size lithium battery do I need covers growing the bank. An AGM bank makes everything here worse — the voltage sags under exactly these loads, which is half the case made in lithium vs AGM.

The DC side: what those watts look like in copper

Watts feel abstract until they become amps at 12V, which is what your cables, fuse and battery terminals experience:

Inverter at full output	Draw from a 12V bank	Manufacturer’s fuse & cable call
1,000W	~92A	—
2,000W	~184A	Renogy 2000W: 250A fuse, 1/0 AWG (included)
2,200W	~202A	GIANDEL: not stated — size as for 2,000W+
3,000W	~276A	Renogy 3000W: 400A fuse, 4/0 AWG (not included)
MultiPlus 12/3000	~215A at its 2,400W	Victron: 400A fuse, 2 × 50mm² per terminal

Amps are computed at 12.8V nominal and 85% full-load efficiency; fuse and cable figures are from each manufacturer’s manual. The practical point: a 3,000W install is welding-cable territory, and the cabling, lugs and Class T fuse are a real second purchase — budget them with the inverter, not after it.

Those same amps decide one more component, if you are fitting a battery monitor: the shunt goes in the battery negative, so the inverter’s draw is the largest current it will ever see. Xantrex publishes 192A at full load and up to 400A on starting surges for its 2000W unit, which is why an inverter rig wants a 500A shunt where a rig without one does not — what size shunt do you need works through both of its ratings.

One caveat on that last column, because the manuals are quoted more often than they are read: each of those cable calls assumes a short run. Renogy’s 1/0 is the three-foot pair in the box. Mount the same 2,000W inverter ten feet from the bank and 1/0 loses about 4% of your 12 volts, which is past the target and two sizes short of what the distance needs. Put your own run length into the DC voltage drop calculator before ordering cable to a figure from a manual.

Why “just buy the big one” backfires

An inverter consumes power by being on. The published idle figures on the units we recommend run from under 10W (Krieger) through 24–30W (GIANDEL, Renogy) to 20W with an 8W search mode (Victron MultiPlus). Take a middle-of-the-road 25W and leave it on around the clock: that is 600Wh a day — roughly 50Ah, half of a 100Ah battery, spent powering nothing.

An oversized inverter idles higher, sits further below its efficient operating range on your actual loads, and cost more to cable. Size to your loads and bank, and put the remote switch where you will actually flip it.

Three worked examples

Weekend couple, one 100Ah battery. Coffee maker in the morning, laptops and lights at night. Biggest simultaneous load ~1,100W, no motor surges worth naming. A 1,000–1,200W inverter fits inside the single battery’s 1,280W ceiling — just — and staying at this size is what makes one battery workable. The moment a microwave joins the list, this becomes a two-battery system.

Two-battery bank, microwave rig. Microwave (1,500W from the outlet) plus a TV and charging, ~1,700W peak. The 2,000W class with 2,560W of bank behind it: the Renogy 2000W with its included cables, or the GIANDEL 2200 where budget leads.

Family fifth wheel, induction cooking. Induction burner and microwave staggered, residential fridge always on — 2,200–2,600W peaks. This is the 3,000W class, and the bank comes first: three 100Ah batteries in parallel or a GC3, then the Renogy 3000W with its 4/0 cable and 400A fuse priced in (how it stacks against Victron’s alternative is in Victron vs Renogy). On a rig like this, also read inverter vs inverter/charger — replacing the converter and inverter with one box starts making sense at this scale, and the charger that refills a bank this size is a serious pedestal load in its own right (30 amp vs 50 amp covers what fits).

The picks, by size class

Full reviews of all seven units we compared, including the dealer-network and inverter/charger options, are in the best RV inverters — and the 3,000W class pick has a dedicated review covering what owners report.

Related guides

• Best RV inverters — the seven units compared on the figures this page sizes against.
• Best RV lithium batteries — BMS ratings, charge limits and warranty terms for the bank side of the equation.
• What size lithium battery do I need? — this page’s twin, for the battery bay.
• Lithium vs AGM — why chemistry decides whether these load numbers work at all.
• Do I need a DC-DC charger? — refilling the bank from the tow vehicle between hookups.
• 30 amp vs 50 amp RV — the shore-power half of the arithmetic.
• The electrical section collects everything published so far.

For how products on this site are selected and what we do not claim about them, see the editorial policy.

Questions worth answering