Generator Size Calculator — Backup Generator Guide

Estimate generator power from running watts, motor-starting loads and headroom. Save locally, export a worksheet, and work offline.

Plan the appliance loads you want to power during an outage with Generator Size Calculator from Backup Generator Guide. Open the calculator from Chrome’s toolbar or use the full-tab view for a larger workspace. It runs offline, so your planning tool remains available without an internet connection. WHAT YOU CAN DO • Start with an example plan or a blank plan. • Add, edit, or remove appliances and enter running watts and extra starting watts. • Include the loads you intend to power together and choose a headroom percentage. • Review continuous power and a starting-event capacity estimate. • Keep one automatically saved local draft, including unfinished entries. • Copy a summary, export your plan as CSV, or print it. • Delete your saved plan when you are finished. YOUR PLAN STAYS ON YOUR DEVICE The extension stores your calculator inputs in the current Chrome profile using local extension storage. Backup Generator Guide does not receive your plan. There are no accounts, analytics, advertising trackers, or remote calculator scripts. The extension does not read other websites or your browsing history. Copy, export, print, and website links run only when you choose them. USE REAL APPLIANCE RATINGS Example wattages are placeholders. Replace them with appliance labels or manufacturer specifications. Extra starting watts means demand above normal running watts. The estimate assumes all listed loads run together and only one motor starts at a time. The default 15% headroom is a planning assumption. This calculator does not assess wiring, voltage compatibility, transfer equipment, installation, or every generator’s motor-starting capability. Confirm the final generator choice with product documentation and a qualified installer. Created by Backup Generator Guide. https://backupgeneratorguide.com/