Battery Storage Sizing Calculator

Work out battery storage sizing instantly with clear inputs, formula shown and shareable results.

About Battery Storage Sizing Calculator

Battery capacity must cover the load energy, grossed up for inverter and round-trip losses and then divided by the usable depth of discharge, since discharging a lithium battery fully shortens its life. The resulting C-rate — power divided by capacity — must be within the cell's continuous discharge rating.

Formulas

Battery sizing

Nominal capacity = load power x hours / system efficiency / depth of discharge

C-rate

C-rate = load power / nominal capacity

Worked example

With the default values below, Battery Storage Sizing Calculator returns Nominal Battery Capacity of 1,234.568. Change any input above and every figure here is recalculated in your browser.

Inputs used

Load To Supportminimum 0 kW: 250 kW
Backup Durationminimum 0.01 hours: 4 hours
Usable Depth Of Dischargeaccepts 1–100 %: 90 %
Inverter And Round-Trip Efficiencyaccepts 1–100 %: 90 %

Results

Nominal Battery Capacity: 1,234.568
Usable Energy At The Load: 1,000.000
Energy Drawn From Battery: 1,111.111
Discharge C-Rate: 0.2025

Step by step

1Values used
2Battery sizing
3C-rate
4Nominal Battery Capacity= 1,234.568
5Usable Energy At The Load= 1,000.000
6Energy Drawn From Battery= 1,111.111
7Discharge C-Rate= 0.2025

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Lithium battery installations present fire and thermal runaway risks and must comply with the applicable electrical and fire safety standards, including ventilation and separation requirements.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Lithium battery installations present fire and thermal runaway risks and must comply with the applicable electrical and fire safety standards, including ventilation and separation requirements.

Frequently Asked Questions

What depth of discharge is appropriate?

Modern lithium iron phosphate systems allow 80-95% with acceptable cycle life. Lead-acid should be limited to 50% for deep-cycle duty, which doubles the capacity needed for the same usable energy.

Why does C-rate matter?

High discharge rates cause voltage sag, heating and accelerated degradation. Systems designed for short high-power bursts need different cells from those designed for long slow discharge.