Free planning tool: no sign-up. Results are estimates, not engineering or installation advice.
UsedItFirst
Free energy calculator

Solar battery size calculator

Estimate nominal storage for an RV, cabin or small off-grid system from daily energy and reserve days.

Built by Calculator version 1.0Updated October 26, 2026

Your inputs

Use the numbers for the exact devices, vehicle or battery system you plan.

Planning model only. Verify manufacturer limits, applicable code and installation requirements before purchase or electrical work.

Your planning estimate

Recommended nominal storage—
Input—
Output—
Planning factor—
Next check—

Enter your numbers and update the estimate.

Use the result

What to do next

The number narrows the market; it does not select a product by itself. Compare continuous and surge limits, charging compatibility, certification for intended use, warranty and total installed cost.

Solar battery size calculatorEstimate watt-hours and amp-hours for your loads.Off-grid solar kitsMatch generation, storage and inverter output.Portable power station calculatorCompare an all-in-one station with a component system.Energy decision centerStart with the use case, not the brand.

Sources

  • NREL PVWatts CalculatorPrimary federal-laboratory tool for estimating photovoltaic energy production. Checked October 26, 2026.
Quick answers

Solar battery size calculator FAQ

How do I calculate solar battery size?

Multiply daily watt-hours by autonomy days, then divide by usable depth of discharge and system efficiency.

Why show both watt-hours and amp-hours?

Watt-hours compare energy across system voltages. Amp-hours are meaningful only when the nominal voltage is also known.

Does this size the solar panels too?

No. The array must be sized separately from local solar resource, season, shade and the energy that needs to be replaced.