Ah sizing is an energy-budget problem: how many watt-hours you need, divided by bus voltage. This guide walks through the battery bank size calculator logic before you buy cells, cables, or fuses.
Benefits
- Transparent chain: Wh needed = load (W) × hours; Ah = Wh ÷ voltage—reproducible on a napkin or in the tool.
- Supports 12 V, 24 V, and 48 V buses common in RV, marine, and small off-grid installs.
- Detail output shows intermediate Wh so you can cross-check against solar-battery-bank planners.
How it works
- Enter total load power in watts and the hours of autonomy you need.
- Set nominal system voltage (12, 24, or 48 V typical).
- Review required Ah; multiply by 1.2–1.5 for inverter loss, depth-of-discharge limits, and aging.
FAQ
How do I calculate battery bank size in Ah?
Multiply load watts by runtime hours to get watt-hours, then divide by system voltage. Example: 500 W × 8 h = 4,000 Wh; at 12 V that is about 333 Ah before safety margin.
Should I size at 12 V or 48 V?
Higher voltage reduces current for the same watts, which can shrink cable size. Ah at the battery is still Wh ÷ V—compare total Wh needs first, then pick a bus architecture your inverter and charger support.
Do I need extra capacity beyond the calculator result?
Yes. Add margin for inverter efficiency, temperature, and not discharging to 100% depth of discharge. Many installers use 1.2–1.5× on the raw Ah figure unless a specific DoD target is modeled.
Technical specifications
- Formula: Ah = (load_W × hours) ÷ voltage_V.
- Inputs: positive W, hours, and V; assumes near-constant load.
- Planning margin: ×1.2–1.5 recommended for loss and DoD unless detailed model applied.
- Related: pair with solar-battery-bank and inverter-sizing tools for full system design.