# Required Battery Capacity Calculator

Work backwards from a backup load and duration to nominal battery capacity.

[Open this tool](https://whatson.pk/battery-size-calculator/)

Category: Solar & Battery

Working backwards from a load and backup duration gives a nominal storage target rather than just a guessed battery count.

Include the intended energy allowance and inverter idle draw, then choose usable discharge within the manufacturer's limits.

## Inputs and controls

* Steady AC load (W). Allowed range: 0.01 to 10000000
* Backup duration (hours). Allowed range: 0.01 to 10000
* Energy allowance (%). Allowed range: 0 to 100
* Bank nominal voltage (V). Allowed range: 0.1 to 2000
* Usable depth of discharge (%). Allowed range: 0.01 to 100
* Inverter efficiency (%). Allowed range: 0.01 to 100
* DC idle consumption (W). Allowed range: 0 to 1000000

## How to use

* Enter steady AC load, backup duration and energy allowance.

* Enter bank nominal voltage, usable depth of discharge, inverter efficiency and DC idle consumption.

* Select Calculate result. Read the returned values alongside the assumptions below before copying, exporting or acting on the result.


## Why use this tool

The calculation connects the storage target directly to the hours and load you want to cover.


## Before relying on the result

Required nominal energy includes the entered allowance and idle draw. Use manufacturer limits to choose usable DoD and discharge capability.


## Tool limitations

Required nominal energy includes the entered allowance and idle draw. Use manufacturer limits to choose usable DoD and discharge capability.

## Questions

### Does capacity alone prove the battery can supply the load?

No. Discharge current, BMS limits and equipment compatibility need a separate check.

### What should I check before using Required Battery Capacity Calculator?

Check Steady AC load, Backup duration, Energy allowance and Bank nominal voltage. Use the exact units shown beside the controls and replace any example values with your own inputs.

Source page last modified (UTC): 2026-10-01T18:56:35+00:00

This profile describes the tool. It does not execute it or supply a professional certification.