Inverter Size Calculator

Our free Inverter Size Calculator takes the guesswork out of selecting the right solar inverter for your off-grid or backup power system. Choosing an undersized inverter causes nuisance tripping and potential damage when high-surge appliances start. Oversizing wastes money on equipment that runs inefficiently at low loads. This tool calculates both continuous running load and peak surge demand — the two critical specifications on every inverter datasheet. The appliance load builder includes five default loads (Refrigerator, TV, Lights, Laptop, Water Pump) that cover the most common residential off-grid scenarios. You can add unlimited custom appliances, specifying running watts and surge watts independently. The peak surge calculation identifies the single highest-surge appliance and adds all other running loads, giving you the worst-case instantaneous peak power demand. Three safety margin options (1.25×, 1.5×, and 2.0×) translate your load totals into inverter capacity recommendations. The tool also recommends inverter type based on your load mix — if motor-driven or electronic loads are present, Pure Sine Wave is recommended; resistive-only loads (heaters, lights, simple chargers) can use lower-cost Modified Sine Wave units. This browser-based inverter sizing tool is used by off-grid solar installers, RV solar system builders, van lifers, boat electrical system designers, and emergency backup power planners. No registration is required and all data stays local in your browser for complete privacy. Understanding your total running load and surge requirements before purchasing an inverter ensures reliable system operation and protects your appliances from power quality issues.

This tool is part of our collection of 100+ free online utilities designed to help developers, designers, and professionals work more efficiently. All tools are completely free, require no registration, and process data locally in your browser for maximum privacy and security. We continuously update and improve our tools based on user feedback to ensure they meet the evolving needs of our global community. Whether you're working on personal projects, professional tasks, or educational assignments, our tools provide reliable solutions that respect your privacy and deliver instant results. The intuitive interface makes it easy for beginners to get started while providing advanced features for experienced users. All tools include comprehensive documentation, example data, and helpful tips to ensure you get the most out of every utility. We believe in making powerful tools accessible to everyone, regardless of technical expertise or budget constraints.