How to Size an Inverter for Your RV: Watt Math Made Simple (2026)

Knowing how to size an inverter for your RV comes down to two questions the marketing never asks: what is the most you will run at once, and can your battery actually feed it? Get the first wrong and appliances trip; get the second wrong and the inverter shuts down mid-use. This guide walks both with the watt math made simple.

Step 1: Add up your largest simultaneous load

Inverter sizing is not about total appliances — it is about the most running at the same instant. List what could plausibly be on together at the worst moment, total their running watts, and note the surge for anything with a motor.

Appliance	Running watts	Surge
Laptop	60	—
Microwave (900W rated)	1,300	1,500
Coffee maker	1,000	—
Compressor fridge start	120	400+

Notice that single high-draw appliances — microwave, kettle, induction hob — set your inverter size, not the sum of small electronics. Most RVs never run two 1,500W appliances at once, so sizing for the largest single one plus headroom is usually right.

Step 2: Add surge headroom

Motors and compressors draw two to three times their running wattage for a fraction of a second at startup. Your inverter’s surge rating must cover that spike, or it trips exactly when the fridge compressor kicks in. A good pure sine inverter lists both a continuous and a surge figure — check the surge against your worst startup, not just the running total. Waveform matters here too, covered in pure sine vs modified sine.

Step 3: Check your battery can feed it — the step people skip

This is where builds fail. An inverter can only deliver what the battery supplies. At 12V, a 2,000W inverter draws about 175A; a 3,000W unit about 260A. Your battery’s BMS has a continuous discharge limit, and if the inverter’s demand exceeds it, the battery shuts down under load.

Many 100Ah LiFePO4 batteries cap at 100A continuous — enough for a 1,000W inverter, not a 2,000W one. Running a big inverter often forces a bigger battery, two in parallel, or a move to 24V, which halves the current. Check the limit against battery sizing, and the voltage logic in watts vs volts vs amps.

Sizing by build type

Build	Inverter	Min battery (12V)
Charging & small electronics	1,000–1,200W	100Ah
Occasional microwave/coffee	2,000W	200Ah
Induction cooking, tools	3,000W	300Ah or 24V

Do not oversize for its own sake — a bigger inverter draws more idle current and needs heavier cable. Size to real use and switch it off when idle. Wiring is in inverter cable sizing; standards at the National Fire Protection Association.

Frequently asked questions

What size inverter do I need for my RV?

Size it to the largest total load you will run at once, then confirm the surge rating covers motor startups. Most RVs land on 2,000W for occasional microwave or coffee use; minimalist builds manage on 1,000–1,200W. Only go to 3,000W for genuine induction cooking or heavy tools.

Why does my inverter shut off under load?

Usually the battery cannot supply the current. A 2,000W inverter needs about 175A at 12V, and many 100Ah batteries cap at 100A, so the BMS cuts out. Check your battery’s continuous discharge rating against the inverter’s draw before blaming the inverter.

Should I oversize the inverter for the future?

Only modestly. A larger inverter draws more idle current and needs heavier cable, so wildly oversizing wastes energy and money. Size to real use with sensible surge headroom, and switch the inverter off at the unit when you do not need AC.

Do I need 12V or 24V for a big inverter?

Above about 2,000W, 24V is worth serious thought — it halves the current for the same power, easing the load on the battery, BMS and cabling. Small 12V builds are simpler; large power-hungry builds benefit from higher voltage.

Last updated: July 24, 2026. Wattage figures are typical; check your appliances’ labels and your battery’s discharge limit.