Quick Answer: Watt-hours to Amp-hours
One watt-hour is approximately 0.08333 amp-hours at 12 V (1 Wh ≈ 0.08333 Ah).
Conversely, 1 Ah = 12 Wh at 12 V.
Formula: Ah = Wh ÷ 12 V
Worked examples
- 100 Wh ≈ 8.333 Ah at 12 V
- 250 Wh ≈ 20.83 Ah at 12 V
- 600 Wh = 50 Ah at 12 V
Method and limitations
Divide watt-hours by the system voltage of 12 V to get amp-hours, the capacity figure printed on lead-acid and LiFePO4 battery labels. Calculations use full-precision constants; answers in this box are rounded for readability (≈ marks a rounded value) and the calculator shows up to 9 significant figures. This is not a fixed unit pair: charge (Ah) becomes energy (Wh) only at a stated voltage — 12 V here. Use the nominal voltage of the cell or pack you have; nominal energy is not the same as usable energy.
Each factor is exact by definition, derived from exact definitions, or a documented conventional value — see the methodology and sources.
Conversion Formula
Divide watt-hours by the system voltage of 12 V to get amp-hours, the capacity figure printed on lead-acid and LiFePO4 battery labels.
This formula uses the system voltage currently set in the calculator (12 V). Change it above and this formula updates with it — the relationship is not a fixed unit pair.
Complete Guide to Watt-hours to Amp-hours Conversion
What is a watt-hour?
A watt-hour (Wh) is an energy rating that already includes voltage, making it the only way to compare batteries across different system voltages and chemistries.
What is an amp-hour?
An amp-hour (Ah) is a charge rating: one ampere delivered for one hour. Lead-acid, AGM and LiFePO4 batteries are labelled in amp-hours because that is how battery capacity has been specified since the earliest automotive systems.
How the Conversion Works
Energy equals charge multiplied by voltage, so watt-hours equal amp-hours times system voltage. A 100 Ah battery in a 12 V system stores 1,200 Wh; the same battery in a 24 V pair-configuration stores 2,400 Wh at the pack level.
Why This Conversion Matters
Off-grid, marine and campervan systems are designed around daily energy consumption in watt-hours, but batteries are sold in amp-hours. Sizing a system without converting between the two is how people end up with a bank that dies halfway through the night.
Scientific Context
Rated capacity depends on discharge rate. Lead-acid capacity is normally quoted at the 20-hour rate; drawing the same battery harder reduces delivered capacity substantially, an effect described by Peukert's law. Lithium chemistries are far less sensitive to discharge rate.
Step-by-Step Conversion Guide
Follow these steps to convert watt-hours to amp-hours manually:
Start with your value in watt-hours
Example: You want to convert 600 Wh
Apply the conversion formula
Use the formula: Ah = Wh ÷ 12 V
Calculate the result
600 Wh = 50 Ah
Verify your answer
Use our calculator above to double-check your manual calculation.
Quick Mental Math Tip
Divide watt-hours by the system voltage of 12 V to get amp-hours, the capacity figure printed on lead-acid and LiFePO4 battery labels.
Common Conversions
Calculated at 12 V (system voltage). Change the value in the calculator above and this table recalculates.
| Watt-hours (Wh) | Amp-hours (Ah) | Amp-hours → Watt-hours |
|---|---|---|
| 100 Wh | 8.33333 | 100 Ah = 1,200 Wh |
| 250 Wh | 20.8333 | 250 Ah = 3,000 Wh |
| 600 Wh | 50 | 600 Ah = 7,200 Wh |
| 1200 Wh | 100 | 1200 Ah = 14,400 Wh |
| 1800 Wh | 150 | 1800 Ah = 21,600 Wh |
| 2400 Wh | 200 | 2400 Ah = 28,800 Wh |
| 3600 Wh | 300 | 3600 Ah = 43,200 Wh |
| 4800 Wh | 400 | 4800 Ah = 57,600 Wh |
When You'll Need This Conversion
Campervan and marine systems
Size a leisure battery bank against your daily watt-hour consumption.
Off-grid solar storage
Match panel output, daily loads and battery amp-hours at your chosen system voltage.
UPS and backup power
Convert backup battery amp-hours into runtime at a known load.
Solar system design
Decide between 12 V, 24 V and 48 V architectures based on current and cable sizing.
Pro Tips for Accurate Conversions
Always state the system voltage
An amp-hour figure without voltage cannot be turned into energy.
Design on usable, not nameplate, capacity
Lead-acid: 50%. LiFePO4: 80–90%.
Go 48 V above about 3 kW
Lower current means thinner cable, less loss and safer connections.
Common Mistakes to Avoid
Comparing 12 V and 24 V amp-hour ratings
The same Ah number represents twice the energy at 24 V.
Convert both to watt-hours before comparing.
Planning around 100% discharge
Deep discharge destroys lead-acid batteries within months.
Size the bank so daily use stays within the safe depth of discharge.
Forgetting inverter losses
DC-to-AC conversion costs 10–15% of stored energy.
Divide AC load energy by 0.85 when sizing the battery.
History & Background
Amp-hour ratings date to the lead-acid battery of 1859 and survived because automotive and marine systems have used them for over a century.
Key Milestones
Gaston Planté invents the lead-acid battery, still the reference for Ah ratings.
Peukert publishes his law relating discharge rate to delivered capacity.
LiFePO4 chemistry is described, later dominating leisure and off-grid storage.
Drop-in lithium replacements push watt-hour comparisons into the mainstream.
Global Usage Today
Amp-hours remain the labelling standard for automotive, marine and off-grid batteries worldwide, while watt-hours dominate portable electronics and EVs.
Frequently Asked Questions
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Conversion factors on this page are either exact by definition, derived from exact definitions, or conventional values in documented use. Each is listed with its source in our conversion methodology and sources, which cites the BIPM SI Brochure, NIST Special Publication 811 and the relevant IEC or national standards. Results are rounded for display only; calculations use full precision.