Use our home battery backup sizing calculator to work out base energy needed. Enter essential load and backup hours — results update.
Formula
const baseKwh = essentialLoadWatts * backupHours / 1000; const adjustedKwh = baseKwh / (inverterEfficiency / 100) * (1 + reserveMargin / 100); const batteriesNeeded = batteryModuleKwh > 0 ? Math.ceil(adjustedKwh / batteryModuleKwh) : 0; const estimatedCost = batteriesNeeded * costPerModule; return { baseKwh, adjustedKwh, batteriesNeeded, estimatedCost };Essential Load
1,200 W
Backup Hours
12 hours
Inverter Efficiency
92 %
Reserve Margin
20 %
Battery Module Size
5 kWh
Installed Cost / Module
4,500 $
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Home Battery Backup Sizing Calculator estimates Base Energy Needed, Recommended Battery Size, Battery Modules Needed, Estimated Installed Cost from Essential Load, Backup Hours, Inverter Efficiency, Reserve Margin, Battery Module Size. It is built for solar, battery, heat pump, EV charging, and quote-comparison decisions; use the output as a decision checkpoint, then confirm current pricing, rules, quotes, or professional advice before committing money.
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The estimate combines Essential Load, Backup Hours, Inverter Efficiency and returns Base Energy Needed, Recommended Battery Size, Battery Modules Needed.
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