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Battery Bank Sizing Calculator

Size a battery for a daily load and days of autonomy — with the usable capacity, not the nameplate.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-27 · v1.0.0

Market
Imperial · sales tax

Nameplate capacity required

11.7 kWh nameplate

Check your inputs

Nameplate needed to deliver the stated usable energy. Real capacity falls with age and with temperature — a bank at 0 °C delivers materially less than its rating.

Energy required at the load
10 kWh
Usable share of nameplate
85.5 %
Depth of discharge
90 %
Round-trip efficiency
95 %
At 48 V nominal
243.66 Ah

For the dimensions entered, expect a nameplate capacity required of 11.7 kWh nameplate. Note that daily load (kwh) sits at the low end of the range this calculator was checked against, so treat the output as indicative rather than settled. Moderate confidence — sound arithmetic, but allow for the variation any real site introduces. Set for United States against IRC 2024. The market selector changes both the units and the code cited.

Add the equipment this sizes

This result is a specification — 11.696 kWh nameplate — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Usable capacity = nameplate × depth of discharge × round-trip efficiency. Lithium iron phosphate DoD 80-100%; lead-acid 50% to preserve cycle life
  • Round-trip efficiency: LiFePO₄ 90-95%; flooded lead-acid 75-85% — manufacturer datasheets

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Frequently asked questions

Why is the nameplate so much bigger than my daily use?
Because you cannot use all of it, twice over. Depth of discharge limits how far the bank may be drawn — 50% on lead-acid — and round-trip efficiency loses energy on the way in and out. A flooded lead-acid bank delivers about 40% of its nameplate as usable energy, so 10 kWh of load needs a 25 kWh bank.
Is lithium worth the price difference?
On usable energy per pound, usually. A LiFePO₄ bank delivers around 85% of nameplate against lead-acid's 40%, so it needs less than half the rated capacity for the same job — and it lasts several times as many cycles at that depth. The headline price per kWh of nameplate is the wrong comparison.
How many days of autonomy do I need?
One for grid-tied backup, where the grid is the real supply and the battery covers an outage. Two to three off-grid in a sunny climate. Four or more where winter cloud persists — but at that point a generator is usually cheaper than the extra battery, because you are sizing for a few days a year.