Quick Answer: Milliamp-hours to Watt-hours
One milliamp-hour equals 0.0037 watt-hours at 3.7 V (1 mAh = 0.0037 Wh).
Conversely, 1 Wh ≈ 270.27 mAh at 3.7 V.
Formula: Wh = (mAh × 3.7 V) ÷ 1,000
Worked examples
- 1000 mAh = 3.7 Wh at 3.7 V
- 2000 mAh = 7.4 Wh at 3.7 V
- 3000 mAh = 11.1 Wh at 3.7 V
Method and limitations
mAh is charge; Wh is energy. They are linked only by voltage: Wh = mAh × V ÷ 1,000. Use the nominal voltage the manufacturer states for the cell or pack — the calculator starts at 3.7 V, a common Li-ion nominal value, but you should select the voltage that matches your battery. 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 (mAh) becomes energy (Wh) only at a stated voltage — 3.7 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
mAh is charge; Wh is energy. They are linked only by voltage: Wh = mAh × V ÷ 1,000. Use the nominal voltage the manufacturer states for the cell or pack — the calculator starts at 3.7 V, a common Li-ion nominal value, but you should select the voltage that matches your battery.
This formula uses the nominal cell voltage currently set in the calculator (3.7 V). Change it above and this formula updates with it — the relationship is not a fixed unit pair.
Charge, voltage and energy
mAh is charge; Wh is energy; voltage connects them. Select the nominal voltage that matches the mAh figure: cell voltage for a single cell, pack voltage for cells in series. If the battery label states Wh, that figure already includes the manufacturer's voltage.
The result is nominal energy. What a device actually receives is lower, by amounts that depend on the charger, conversion electronics, temperature and battery age — this page does not assume a figure. Aviation rules are written in Wh; check the current rules with your airline.
For large batteries, the amp-hours to watt-hours converter covers 12/24/48 V systems.
Constants and their sources are listed on the methodology page.
Complete Guide to Milliamp-hours to Watt-hours Conversion
What is a milliamp-hour?
A milliamp-hour (mAh) is a quantity of electric charge: one milliampere for one hour, or 3.6 coulombs. It is not energy.
What is a watt-hour?
A watt-hour (Wh) is energy: one watt for one hour, or 3,600 J. It already includes voltage, so it compares batteries of different voltages fairly.
How the Conversion Works
Energy = charge × voltage. Wh = mAh × V ÷ 1,000. Nominal voltage is a representative average across the discharge curve; the actual voltage changes as the battery discharges.
Why This Conversion Matters
Battery marketing often uses mAh while energy budgets, comparisons and transport rules use Wh. Converting requires the right voltage, and the result is nominal rather than usable energy.
Scientific Context
Lithium-ion cell voltage typically falls from around 4.2 V when full towards about 3 V near empty, depending on chemistry; the nominal value summarises that curve. Chemistries such as LiFePO4 and NiMH have different nominal voltages.
Step-by-Step Conversion Guide
Follow these steps to convert milliamp-hours to watt-hours manually:
Start with your value in milliamp-hours
Example: You want to convert 3000 mAh
Apply the conversion formula
Use the formula: Wh = (mAh × 3.7 V) ÷ 1,000
Calculate the result
3000 mAh = 11.1 Wh
Verify your answer
Use our calculator above to double-check your manual calculation.
Quick Mental Math Tip
At 3.7 V, every 1,000 mAh is 3.7 Wh: 5,000 mAh ≈ 18.5 Wh. At 7.4 V (two cells in series) the same mAh is twice the Wh.
Common Conversions
Calculated at 3.7 V (nominal cell voltage). Change the value in the calculator above and this table recalculates.
| Milliamp-hours (mAh) | Watt-hours (Wh) | Watt-hours → Milliamp-hours |
|---|---|---|
| 1000 mAh | 3.7 | 1000 Wh = 270,270 mAh |
| 2000 mAh | 7.4 | 2000 Wh = 540,541 mAh |
| 3000 mAh | 11.1 | 3000 Wh = 810,811 mAh |
| 5000 mAh | 18.5 | 5000 Wh = 1,351,350 mAh |
| 10000 mAh | 37 | 10000 Wh = 2,702,700 mAh |
| 20000 mAh | 74 | 20000 Wh = 5,405,410 mAh |
| 26800 mAh | 99.16 | 26800 Wh = 7,243,240 mAh |
| 50000 mAh | 185 | 50000 Wh = 13,513,500 mAh |
When You'll Need This Conversion
Comparing batteries fairly
Convert mAh ratings at different voltages to Wh before comparing them.
Finding the Wh figure for travel
Get the Wh value aviation rules use, then check the current rules with your airline.
Runtime estimates
Divide Wh by a device's average power draw in W for an upper-bound runtime.
Pro Tips for Accurate Conversions
Prefer a printed Wh figure
When the label states Wh, it is more reliable than recalculating from mAh.
mAh only compares at equal voltage
Two batteries with the same mAh at different voltages store different energy.
Common Mistakes to Avoid
Using USB output voltage (5 V)
Power-bank mAh ratings are normally stated at cell voltage, not output voltage.
Use the nominal cell or pack voltage that the mAh rating refers to.
Treating nominal Wh as usable Wh
Losses and battery management reduce what reaches the device.
Treat the result as an upper bound.
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.