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Battery Depth of Discharge Calculator

Enter the battery capacity and depth of discharge to get the usable capacity.

How it is calculated

The tool takes the battery's rated capacity C and the depth of discharge DoD you are willing to use, as a percentage from 0 to 100, and splits the capacity in two:

usable = C × DoD ÷ 100
reserved = C − usable

The capacity can be in any one unit (Ah, Wh or kWh) and the answers come back in that same unit, with no unit label added. Capacity must be above 0; a DoD below 0 or above 100 returns nothing. The tool applies the DoD limit you choose and does not know your battery's chemistry, age, temperature or discharge rate, all of which change the real usable capacity. To work in reverse, divide the energy you need by DoD ÷ 100 to find the rated capacity to buy.

Worked example

A 200 Ah battery bank is limited to 60% depth of discharge. Usable capacity = 200 × 60 ÷ 100 = 120.00 Ah. The reserve left in the battery is 200 − 120 = 80.00 Ah. If a load needs 150 Ah between charges, this bank is too small; at 60% DoD you would need at least 150 ÷ 0.60 = 250 Ah of rated capacity.

Try this example →

Common mistakes

  • Entering the DoD as a fraction, such as 0.6. The field is in percent, so 0.6 gives only 0.6% usable capacity (1.20 for a 200 Ah battery).
  • Sizing a battery bank to the nameplate capacity instead of the usable part. A 200 Ah battery at 60% DoD supplies 120 Ah, not 200.
  • Using a DoD above what the manufacturer recommends and expecting the same life. A deeper discharge is accepted by the tool, but it shortens the cycle life of the battery.
  • Mixing units, for example entering capacity in Ah and comparing the result with a load in Wh. Convert with the battery voltage first.
  • Treating the reserved value as extra power you can spend. It is the energy you decided to leave in the battery to protect it.

About this calculator

Depth of discharge (DoD) is the percentage of a battery's total capacity that you allow to be drawn down in a cycle, and usable capacity = total capacity × DoD%, with the remainder held in reserve. Discharging beyond the recommended DoD accelerates degradation and shortens cycle life, which is why manufacturers specify a safe maximum for each chemistry.

The safe DoD varies sharply by battery type: flooded lead-acid batteries are typically limited to 50% DoD, while lithium-ion (including LiFePO4) can regularly handle 80–100% DoD. Solar and off-grid system designers use this calculator to size a battery bank so the usable capacity — not the nameplate capacity — meets actual energy needs.

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Comments (1)

  • Editorial team

    The result is in whatever unit you typed, so convert before sizing a load. A 200 Ah, 12 V bank at 60% DoD gives 120 Ah of usable capacity, which is 1,440 Wh. A steady 100 W load would drain that in about 14 hours, and inverter losses would shorten it further. The tool does not include those losses. Which battery chemistry are you planning around, and what DoD limit does its maker give?

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