Quick Answer: Amp-hours to Watt-hours
One amp-hour equals 12 watt-hours at 12 V (1 Ah = 12 Wh).
Conversely, 1 Wh ≈ 0.08333 Ah at 12 V.
Formula: Wh = Ah × 12 V
Worked examples
- 7 Ah = 84 Wh at 12 V
- 12 Ah = 144 Wh at 12 V
- 20 Ah = 240 Wh at 12 V
Method and limitations
Ah is charge, not energy. Wh = Ah × system voltage. The calculator starts at 12 V; select 24 V, 48 V or your battery's actual nominal voltage (for example 12.8 V or 51.2 V for LiFePO4) to match your system. 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
Ah is charge, not energy. Wh = Ah × system voltage. The calculator starts at 12 V; select 24 V, 48 V or your battery's actual nominal voltage (for example 12.8 V or 51.2 V for LiFePO4) to match your system.
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.
From Ah label to usable storage
Bank energy = voltage × Ah. Series connections add voltage, parallel connections add Ah: two 12 V 100 Ah batteries are 2,400 Wh nominal either way.
Nominal Wh is not automatically usable Wh. Allowed depth of discharge, battery-management limits, temperature and inverter losses are separate questions, answered by your battery and inverter datasheets rather than a general percentage.
The home battery storage guide and the Home Energy guide cover how storage capacity relates to household consumption.
Constants and their sources are listed on the methodology page.
Complete Guide to Amp-hours to Watt-hours Conversion
What is an amp-hour?
An amp-hour (Ah) is a quantity of charge: one ampere for one hour, or 3,600 coulombs. Lead-acid, AGM and LiFePO4 batteries are commonly labelled in Ah.
What is a watt-hour?
A watt-hour (Wh) is energy, one watt for one hour. kWh = Wh ÷ 1,000 is the unit used for home batteries and electricity consumption.
How the Conversion Works
Multiply Ah by the battery or bank voltage. Series connections add voltage; parallel connections add Ah.
Why This Conversion Matters
Storage is planned against energy use in kWh, while many batteries are sold by Ah. The conversion needs a voltage, and the result is nominal energy — usable energy, inverter losses and battery management are separate questions.
Scientific Context
Rated Ah is measured at a specified discharge rate and temperature. Lead-acid capacity falls noticeably at higher discharge rates (Peukert effect); lithium chemistries are less sensitive.
Step-by-Step Conversion Guide
Follow these steps to convert amp-hours to watt-hours manually:
Start with your value in amp-hours
Example: You want to convert 20 Ah
Apply the conversion formula
Use the formula: Wh = Ah × 12 V
Calculate the result
20 Ah = 240 Wh
Verify your answer
Use our calculator above to double-check your manual calculation.
Quick Mental Math Tip
100 Ah is 1.2 kWh at 12 V, 2.4 kWh at 24 V and 4.8 kWh at 48 V — the Ah figure alone says nothing until the voltage is known.
Common Conversions
Calculated at 12 V (system voltage). Change the value in the calculator above and this table recalculates.
| Amp-hours (Ah) | Watt-hours (Wh) | Watt-hours → Amp-hours |
|---|---|---|
| 7 Ah | 84 | 7 Wh = 0.583333 Ah |
| 12 Ah | 144 | 12 Wh = 1 Ah |
| 20 Ah | 240 | 20 Wh = 1.66667 Ah |
| 50 Ah | 600 | 50 Wh = 4.16667 Ah |
| 75 Ah | 900 | 75 Wh = 6.25 Ah |
| 100 Ah | 1,200 | 100 Wh = 8.33333 Ah |
| 150 Ah | 1,800 | 150 Wh = 12.5 Ah |
| 200 Ah | 2,400 | 200 Wh = 16.6667 Ah |
| 300 Ah | 3,600 | 300 Wh = 25 Ah |
| 400 Ah | 4,800 | 400 Wh = 33.3333 Ah |
When You'll Need This Conversion
Home and off-grid storage
Express battery-bank capacity in Wh or kWh to compare with daily consumption figures.
Leisure and marine batteries
Convert a 12 V Ah label to Wh before comparing with appliance energy use.
Comparing 12/24/48 V designs
Check that two banks with different Ah ratings store the same or different energy.
Pro Tips for Accurate Conversions
Quote Wh with "nominal"
Nominal Wh is the label value; usable Wh is what the system lets you draw.
Use the datasheet for usable capacity
Depth-of-discharge limits differ by chemistry and manufacturer.
Common Mistakes to Avoid
Comparing Ah across voltages
100 Ah at 48 V stores four times the energy of 100 Ah at 12 V.
Compare in Wh.
Adding Ah in series
Series connection raises voltage; the Ah rating stays the same.
Bank Wh = total voltage × Ah (series) or voltage × total Ah (parallel).
Assuming a fixed efficiency
Inverter, battery and wiring losses vary by equipment and load.
Use your own equipment data.
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.