What this calculator does
This tool estimates how large a battery bank (in amp-hours) you need to power a given load for a set number of hours, which is useful for backup power, solar, and off-grid system planning.
How the calculation works
Total energy needed is load in watts multiplied by backup hours, giving watt-hours. That figure is divided by the system voltage, the usable depth of discharge (batteries shouldn’t normally be fully drained), and overall system efficiency (accounting for inverter and wiring losses) to get the required amp-hour capacity. A margin is added to the recommended size for a safety buffer.
This is a general planning estimate. Battery chemistry, temperature, and manufacturer specifications can all affect real-world usable capacity, so consult your battery and inverter documentation for a final sizing decision.