Watt-hours are not printed on every label—you derive them from amp-hours and voltage. This guide shows how to calculate watt-hours from amp-hours with the nominal volts your pack actually runs at.
Benefits
- Formula: Wh = Ah × nominal voltage.
- Works for 12 V AGM, 48 V solar, and 3.7 V lithium cells.
- Reverse check: Ah = Wh ÷ V when sizing from an energy target.
How it works
- Read amp-hours from the battery nameplate or datasheet.
- Multiply by nominal system voltage—not peak charge voltage alone.
- Read watt-hours; divide by 1,000 for kWh on large banks.
FAQ
How do I calculate watt-hours from amp-hours?
Wh = Ah × V. Example: 280 Ah LiFePO4 at 12.8 V nominal → 280 × 12.8 = 3,584 Wh (3.584 kWh). Use the voltage the load sees during discharge, typically nominal pack voltage.
Should I use fully charged or nominal voltage?
Use nominal or average discharge voltage for energy estimates—12.8 V for LiFePO4 12 V packs, 12 V for lead-acid, 48 V for a 48 V nominal bus. Full-charge voltage overstates Wh slightly; nominal is standard for sizing comparisons.
What if my spec only lists mAh?
Convert to Ah first: mAh ÷ 1,000. Then Wh = Ah × V. A 10,000 mAh 11.1 V (3S) pack → 10 Ah × 11.1 V = 111 Wh. Same math, smaller numbers.
Technical specifications
- Wh = Ah × nominal_V.
- kWh = (Ah × V) ÷ 1,000.
- Usable Wh ≈ rated Wh × depth_of_discharge.
- Related: ah-to-wh-converter, wh-to-ah, battery-bank-size.