This means you need an inverter with at least 2. 5 kW capacity to handle this load comfortably, factoring in efficiency losses and a safety margin. Use our online tool Watt to Amp Calculator (Single & Three-Phase): Best ToolAn inverter needs to supply two needs: Peak or surge power, and the typical or usual power. Surge is the maximum power that the inverter can supply, usually for only a short time (usually no longer than a second unless specified in the inverter's specifications). Now, when. A straightforward method to calculate inverter size is: Inverter Size (VA) = Total Wattage (W) / Power Factor (0. Factors like appliance efficiency, startup currents, and future expansion should also be considered before. Choosing the right solar inverter size is critical—and one of the most common questions: what solar inverter size do I need? Whether you are installing a rooftop system in California, powering a remote cabin in Alberta, or sizing for a community center in Rajasthan, getting it right means. Calculate the right inverter size for your power needs Combined wattage of all devices you want to run Motors and compressors can surge 2-3x on startup Motor loads require higher surge capacity Choosing the right inverter size is critical for any off-grid, RV, or backup power system.