Inverter size calculator

What size inverter do you need?

Add up the AC appliances you'll run at the same time and the biggest startup surge. The calculator picks a standard inverter size with headroom.

Running watts at once

Everything that could be on together. Example: kettle (if any), laptop, TV.

Largest startup surge (W)

Motors and compressors start at 2–3× their running watts.

Battery voltage

Inverter size—W

Continuous needed—W

Battery draw at full load—A at

Sized with 25% headroom over continuous load and assumes the inverter surges to 2× its rating.

Gear that fits this result

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How inverter sizing works

An inverter has two ratings. The continuous rating is what it can deliver all day. The surge rating, usually about twice the continuous rating for a few seconds, covers the jolt that motors and compressors need to start.

Inverter size ≥ Running watts × 1.25, and surge rating ≥ largest startup watts

The extra 25% keeps the inverter out of its hottest, least efficient range and leaves room for something you forgot. Running an inverter at its limit for long periods shortens its life.

Typical appliance watts

Appliance	Running watts	Startup watts
Laptop charger	45–100	same
TV (LED, 32–50")	50–120	same
Blender	300–600	600–1,200
Microwave (700W cooking)	1,000–1,200	1,200–1,500
Electric kettle	1,000–1,500	same
Hair dryer	1,000–1,800	same
Induction cooktop	1,200–1,800	same
RV air conditioner (13,500 BTU)	1,300–1,800	2,500–3,500

Heating appliances like kettles and hair dryers draw their full wattage the whole time but don't surge. Anything with a motor or compressor surges. A soft-start kit on an air conditioner can cut its startup surge by more than half.

Pure sine wave vs. modified sine wave

Pure sine wave inverters produce power like a wall outlet. Modified sine wave inverters are cheaper, but they can make motors run hot, cause audio buzz, and damage some chargers and medical devices. For a van, boat or RV, pure sine wave is the safe default.

Don't forget the battery side

A 2,000W inverter at full load pulls around 185A from a 12V battery. That needs short, heavy cables, a properly rated fuse, and a battery bank that can supply that current. Lithium batteries list a maximum continuous discharge, often 100A per 100Ah battery, so you may need more than one battery just to feed the inverter.

Frequently asked questions

What size inverter do I need to run a microwave?

A 700W microwave actually draws about 1,000–1,200W. Plan on at least a 1,500W pure sine wave inverter, or 2,000W if anything else runs at the same time.

Can I run an air conditioner on an inverter?

Yes, with a 3,000W inverter or a 2,000W unit paired with a soft-start kit. The bigger limit is battery capacity: an RV air conditioner uses roughly 1,300–1,800Wh every hour it runs.

Does a bigger inverter waste power?

Every inverter draws some power just being on, often 10–40W for larger models. Oversizing a lot wastes energy overnight. Turn it off when you don't need AC, or pick a model with a low-power standby mode.

How many batteries do I need for a 2,000W inverter?

At 12V, a 2,000W inverter can pull about 185A. Most 100Ah lithium batteries are rated for 100A continuous, so two in parallel is the practical minimum to run it near full load.