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Amp-hours to watt-hours converter
Convert battery amp-hours (Ah) to watt-hours (Wh) and back for 12 V, 12.8 V LiFePO4, 24 V, 48 V and single lithium cells, with nominal voltage guidance.
Results
| Energy | 1,280 Wh |
|---|---|
| Energy | 1.28 kWh |
| Same charge in mAh | 100,000 mAh |
About this calculator
Batteries get labelled two ways. Amp-hours (Ah) measure charge, and watt-hours (Wh) measure energy. Watt-hours is the number you can compare across batteries, because 100 Ah at 12 V and 100 Ah at 48 V store very different amounts of energy: 1,280 Wh versus 5,120 Wh.
Use this converter to compare a deep-cycle battery against a portable power station, or to work out how many phone-style mAh a power bank really holds at its cell voltage.
How to use it
- Choose the direction: Ah → Wh or Wh → Ah.
- Enter the number from the label or spec sheet.
- Enter the battery's nominal voltage, not the charging voltage. Use 12.8 V for 12 V-class LiFePO4 and 12 V for lead-acid.
- Use the Wh result in the runtime and sizing calculators.
The formula
Wh = Ah × V and Ah = Wh ÷ V, using the battery's nominal voltage.
A battery's voltage changes as it discharges. Nominal voltage is the average across the discharge, which is why manufacturers use it to calculate rated Wh.
Worked example (default values)
Inputs
| Convert | Amp-hours → watt-hours |
|---|---|
| Value to convert | 100 Ah or Wh |
| Nominal battery voltage | 12.8 V |
Results
| Energy | 1,280 Wh |
|---|---|
| Energy | 1.28 kWh |
| Same charge in mAh | 100,000 mAh |
Tips and common mistakes
Common nominal voltages: LiFePO4 is 3.2 V per cell, so 4 cells = 12.8 V, 8 cells = 25.6 V and 16 cells = 51.2 V. Lead-acid is 2 V per cell, so 6 cells = 12 V. Lithium-ion NMC and 18650/21700 cells are about 3.6-3.7 V.
Power banks: a "20,000 mAh" power bank is rated at its internal cell voltage (about 3.7 V), so it holds about 74 Wh. Converting up to 5 V USB output costs another 10-20%, which is why it can't fill four 5,000 mAh phones.
Frequently asked questions
How many watt-hours is a 100Ah battery?
A 12 V lead-acid battery holds 1,200 Wh. A 12.8 V LiFePO4 battery holds 1,280 Wh. At 24 V it's about 2,560 Wh, and at 48 V (51.2 V LiFePO4) about 5,120 Wh. Only part of that is usable: about 50% for lead-acid and 80-100% for LiFePO4.
Can I bring a power bank on a plane?
Airlines generally allow lithium batteries up to 100 Wh in carry-on bags, with 100-160 Wh needing airline approval. Check your airline's current rules. This converter tells you which category your battery falls into.
Is mAh the same as Ah?
Yes. 1 Ah = 1,000 mAh. mAh is just used for smaller batteries.
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Estimates for planning only, based on the assumptions shown. Real-world performance varies with equipment, temperature and installation. Updated October 19, 2026. See our methodology.