Most power-sizing advice online is either a spec sheet, a sales page, or a forum argument. When you're deciding what battery gets your family through a blackout — or what system goes into a van you'll live in — you need a number, and you need to know where it came from.
Every WattNeeded tool answers one question, shows every step of its math on the same page, and runs entirely in your browser. No sign-up, no email capture, nothing sent to a server.
Losses are never hidden. Inverters eat ~15%. Batteries age. Solar panels underperform their label. Our numbers include all of it, which is why they're bigger than the marketing's.
Headroom is explicit. When we add 20% margin, the results panel says so and shows the pre-margin number too.
Assumptions are editable. Typical wattages get you started; your appliance labels beat our defaults, and every field accepts your numbers.
Region-aware, locally. Currency, terminology (RV vs motorhome) and solar defaults adapt to a region setting — detected from your browser's language, switchable top-right, and stored on your device only. It is never sent anywhere; price ranges are rough market conversions, not live exchange rates.
Some product recommendations may become affiliate links — meaning we earn a commission if you buy, at no cost to you. Two promises: recommendations are computed from your sizing result before any commission is considered, and the math never changes because of who pays. If a tool ever tells you that you need less than you thought, that's the answer you'll get.
Contact details will appear here when the site goes live — corrections to wattage assumptions are especially welcome.