What size inverter do I need for an off-grid cabin?
Inverter sizing is about peak simultaneous load, not the sum of every appliance you own. An undersized inverter trips when the fridge and the coffee maker coincide; an oversized one costs more up front and quietly taxes the battery with idle draw every hour it is on.
The two numbers that matter: continuous watts for what runs together, and surge capability for the biggest motor start on top of everything already running.
How it works
Walk your real scenarios - morning, cooking, evening - and find the worst realistic overlap; that plus margin is your continuous requirement. Then add the largest motor start (well pump, fridge compressor, power tools) on top of the running baseline: motors briefly draw several times their nameplate watts, and the inverter's surge rating must cover it.
Two often-missed factors: idle consumption - a big inverter burns watts around the clock doing nothing, which a small cabin battery feels - and the battery side, since every watt the inverter delivers is current the bank's BMS must be rated to supply. Pure sine wave output is the default for anything with motors or electronics.
Common questions
Continuous versus surge rating - which do I size on?
Both, separately. Continuous covers your worst realistic overlap of running loads; surge covers the largest motor start layered on top. Either one undersized produces the same symptom: the inverter cuts out.
Does an oversized inverter hurt anything?
It costs more and idles hungrier - real energy on a small system running around the clock. Some cabins run a big inverter only during high-load hours, or add a small always-on unit for the base load.
Pure sine or modified sine?
Pure sine. Motors, compressors, and most electronics run cooler and quieter on it, and some devices simply misbehave on modified sine. The price gap has mostly closed.
How does the battery limit inverter choice?
Inverter watts divided by battery voltage is current the bank must legally deliver - continuously and during surge. The checks compare exactly that against the BMS ratings of the batteries you pick.
Pick an inverter and battery bank in the builder and the checks verify draw and surge against the bank's BMS limits before you buy.
Open the builderThese guides are educational and qualitative on purpose - the numeric answers depend on your exact components, and the builder computes them with every formula shown. Always verify a final design with a licensed professional.