For study estimates only, not engineering design
Backup Generator Size Calculator
Estimate a planning load from the equipment totals you enter, the largest additional starting surge, and your chosen reserve margin. The core calculation is free—no login required.
Your planning scenario
Use the planning values to begin a conversation with a qualified generator professional. A product rating above this number is not automatically suitable: starting behavior, nonlinear loads, load sequencing, derating, fuel, transfer equipment, grounding, protection, noise, emissions, and local rules still matter.
Safety boundary: educational planning only—not a generator selection, quotation, wiring instruction, installation design, code-compliance determination, or promise of performance. Do not connect a generator to a building without approved transfer equipment and qualified installation. Verify every load and requirement with manufacturer data and the authority having jurisdiction.
