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Energy Calculators

Battery Bank Size Calculator

Verified formula Updated Jun 2026 Private — runs on your device

Enter details
Wh
%
V
Verified formula Private

Battery capacity needed

667

For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.

How to use the Battery Bank Size Calculator

The Battery Bank Size Calculator works out your battery capacity needed in an instant. Enter daily energy use, days of backup and depth of discharge and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.

  1. Enter the daily energy use.
  2. Enter the days of backup.
  3. Enter the depth of discharge.
  4. Enter the battery bank voltage.
  5. Read off your battery capacity needed — the calculator updates automatically, with no button to press.

Formula

The Battery Bank Size Calculator uses the formula:

Battery capacity needed = Daily energy use × Days of backup ÷ (Depth of discharge ÷ 100 × Battery bank voltage)

Worked example

For example, with daily energy use of 2,000 Wh, days of backup of 2, depth of discharge of 5% and battery bank voltage of 12 V, the battery capacity needed is 667.

Inputs used
Daily energy use 2,000 Wh
Days of backup 2
Depth of discharge 5%
Battery bank voltage 12 V
Results
Battery capacity needed 667

Results are estimates for educational use, not professional advice.

Frequently asked questions

Capacity in Ah = daily watt-hours × days of backup ÷ (depth of discharge × voltage). 2000 Wh for 2 days at 50% DoD on 12 V needs about 667 Ah.

It is how much of the battery you safely use. Discharging only to 50% extends battery life, so you need more total capacity.

Autonomy days cover cloudy spells with no charging. More backup days mean a larger, costlier battery bank.

Yes. Lithium batteries tolerate deeper discharge than lead-acid, so they often need less rated capacity for the same usable energy.

The Battery Bank Size Calculator uses the formula: Battery capacity needed = Daily energy use × Days of backup ÷ (Depth of discharge ÷ 100 × Battery bank voltage). For example, with daily energy use of 2,000 Wh, days of backup of 2, depth of discharge of 5% and battery bank voltage of 12 V, the battery capacity needed is 667.

Enter the daily energy use. Enter the days of backup. Enter the depth of discharge. Enter the battery bank voltage. Read off your battery capacity needed — the calculator updates automatically, with no button to press.

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