Amp-hours measure charge; watt-hours measure energy. This guide shows how to calculate Wh from Ah and voltage—bank capacity, nominal bus V, and stored energy for apples-to-apples comparisons.
Benefits
- Single-step: Wh = Ah × V (multiply, no unit tricks).
- Works for single blocks and summed series/parallel banks.
- Outputs kWh by dividing Wh by 1,000 for utility-scale reads.
How it works
- Confirm total bank Ah (parallel adds Ah; series keeps Ah).
- Use nominal system voltage (series adds V; parallel keeps V).
- Multiply Ah × V for Wh—compare packs at different voltages fairly.
FAQ
How do I calculate Wh from Ah and voltage?
Wh = Ah × V. Example: 280 Ah at 48 V → 280 × 48 = 13,440 Wh (13.44 kWh). For 200 Ah at 12 V: 200 × 12 = 2,400 Wh. Voltage must match the Ah rating bus—do not mix cell V with pack Ah from a different string.
How do series and parallel strings affect Wh?
Series raises voltage; parallel raises Ah. A 4S2P 100 Ah 3.2 V LiFePO4 block: 12.8 V × 200 Ah = 2,560 Wh. Calculate Wh after resolving total bank Ah and system V—not per-cell mAh alone unless you rebuild the string math.
Should I use nominal or fully charged voltage?
Use nominal bus voltage for planning—12 V lead-acid, 48 V LiFePO4 nominal, 3.7 V Li-ion cell. Float and charge voltages are higher temporarily; energy comparisons across products use nominal V unless the datasheet specifies otherwise.
Technical specifications
- Wh = capacity_Ah × nominal_V.
- kWh = Wh ÷ 1,000.
- Series: V adds; parallel: Ah adds (for Wh, use totals).
- Related: battery-energy-calculator-wh, ah-to-wh, battery-bank-size.
Two inputs, one energy number
Every battery label lists amp-hours; the missing variable for energy is voltage. Calculate Wh from Ah and voltage by multiplying—no conversion tables required. A 400 Ah 12 V bank and a 100 Ah 48 V bank both store 4,800 Wh. Procurement teams that sort only by Ah overpay or under-size when bus voltage changes.
Build bank totals before multiplying
Stacking modules in series increases voltage; paralleling increases Ah. Resolve the as-installed Ah and V at the main bus, then Wh = Ah × V. Per-module math is fine for BOM checks, but interconnection and inverter limits care about the whole bank Wh at the service voltage.
Wh feeds the next calculators
Divide Wh by load watts for runtime estimates, or apply DoD % for usable energy. When daily load is stated in kWh, compare directly after converting bank Wh to kWh. Chain to Battery Runtime for hours, Battery Bank Size when working backward from load budgets, and Ah to Wh when sources quote mAh cell data.