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Solar Battery Capacity Calculator

Use our solar battery capacity calculator to find battery size in kWh and Ah from daily use, back up days, DoD, and system eff.

Battery Energy = (Daily Energy × Backup Days) ÷ (DoD × Efficiency)
Wh/day
Total energy your appliances use per day
days
Days the battery should supply the load without solar generation
V
%
Percentage of the battery's rated capacity that can be safely used
%
Accounts for energy losses in the inverter and power-conversion system
Solar Battery Capacity — Formula Reference
FormulaMeaning
Battery Energy (Wh) = (Daily Energy × Backup Days) ÷ (DoD × Efficiency)Required usable energy storage, accounting for DoD and conversion losses
Battery Capacity (kWh) = Battery Energy ÷ 1000Energy capacity in kilowatt-hours
Battery Capacity (Ah) = Battery Energy ÷ Battery VoltageBattery-bank capacity in amp-hours at the chosen system voltage
⚠ DoD and System Efficiency reduce the effectively usable energy from a battery's rated capacity — this calculator divides by both to size the nominal capacity needed to actually deliver your stated daily energy over the backup period.
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A battery can save sun power for later use. But how big should it be? Our tool can help. It uses daily power use, back up days, volts, DoD, and loss. You get the size in kWh and Ah.

Think of the battery as a tank. Your daily load is the water you use. More use needs more tank space. More back up days also need more space.

Battery Size Formula

Use this core math:

Battery Energy (Wh) = (Daily Energy × Back Up Days) ÷ (DoD × Eff.)

Turn each rate to a decimal.

DoD = DoD% ÷ 100

Eff. = Eff.% ÷ 100

Then:

Battery Size (kWh) = Battery Energy (Wh) ÷ 1000

For Ah:

Battery Size (Ah) = Battery Energy (Wh) ÷ Battery Volts

How to Use the Online Tool

  1. Enter daily power use in Wh/day.
  2. Enter the back up days you need.
  3. Enter battery volts, such as 12 V, 24 V, or 48 V.
  4. Enter DoD and system eff. Use 80% and 90% for a test.
  5. Hit calc. You’ll get the kWh and Ah size.

Example Battery Size Math

Say a home uses 3,000 Wh each day. It needs two days of back up. The bank is 48 V. DoD is 80%. Eff. is 90%.

DoD = 80 ÷ 100 = 0.80

Eff. = 90 ÷ 100 = 0.90

Battery Energy = (3,000 × 2) ÷ (0.80 × 0.90)

Battery Energy = 6,000 ÷ 0.72 = 8,333.33 Wh

Battery Size = 8,333.33 ÷ 1000 = 8.33 kWh

Battery Size = 8,333.33 ÷ 48 = 173.61 Ah

So, you need 8.33 kWh, or 173.61 Ah at 48 V.

Battery Size Guide

A battery tool finds the storage you need. A solar panel tool finds the PV size. A solar and battery tool may do both. But each task has its own math.

This tool can help with off-grid use and a solar set-up. It can also help with a solar battery storage plan.

Final Verdict

This battery size tool can cut guesswork. Start with daily power use. Add back up days, DoD, volts, and loss. Then check the kWh and Ah result. Our tool makes this task fast and clear.

FAQs

What does this tool do?

It finds the battery size needed for a set load and back up time.

How do I find battery size?

Use daily power, back up days, DoD, loss, and battery volts.

Is this a solar battery storage tool?

Yes. It gives a basic storage size for a solar power set-up.

Is a panel and battery tool the same?

No. Panel size and battery size are two parts of the same plan.

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