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 = 270.27027 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
Charge alone is not energy. Multiply milliamp-hours by the nominal cell voltage — 3.7 V for standard lithium-ion — and divide by 1,000 to get watt-hours. Calculations use full-precision constants; displayed values are rounded to at most 9 significant figures. This is not a fixed unit pair. The result depends on nominal cell voltage, so always state the nominal cell voltage (3.7 V here) alongside the answer.
Each factor is exact by definition, derived from exact definitions, or a documented conventional value — see the methodology and sources.
Conversion Formula
Charge alone is not energy. Multiply milliamp-hours by the nominal cell voltage — 3.7 V for standard lithium-ion — and divide by 1,000 to get watt-hours.
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.
Complete Guide to Milliamp-hours to Watt-hours Conversion
What is a Milliamp-hours?
A milliamp-hour (mAh) measures electric charge: one milliampere flowing for one hour. Phone, tablet and power bank marketing uses it because the numbers look impressive, but it says nothing about energy on its own.
What is a Watt-hours?
A watt-hour (Wh) measures energy. It already includes voltage, which makes it the only fair way to compare batteries of different chemistries and cell configurations — and the basis of aviation safety limits.
How the Conversion Works
Energy equals charge multiplied by voltage. Milliamp-hours become watt-hours by multiplying by the nominal cell voltage and dividing by 1,000 to convert milli-units. This calculator uses 3.7 V, the nominal voltage of a standard lithium-ion cell; substitute 3.2 V for LiFePO4 or 1.2 V for NiMH.
Why This Conversion Matters
Airlines, shipping regulations and honest product comparisons all run on watt-hours. A power bank advertised as 20,000 mAh and a laptop battery advertised as 60 Wh sound unrelated, but converted they are 74 Wh and 60 Wh — nearly the same battery.
Scientific Context
Nominal voltage is an average across the discharge curve. A lithium-ion cell starts near 4.2 V and ends near 3.0 V, and 3.7 V represents the working midpoint. Using the peak voltage instead overstates capacity by roughly 13%.
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
Charge alone is not energy. Multiply milliamp-hours by the nominal cell voltage — 3.7 V for standard lithium-ion — and divide by 1,000 to get watt-hours.
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
Airline battery compliance
Carry-on lithium batteries are limited to 100 Wh without airline approval, and 160 Wh with it.
Comparing power banks honestly
Convert competing mAh claims into watt-hours before deciding.
Device runtime planning
Divide watt-hours by device power draw to estimate hours of use.
Tool battery packs
18 V tool packs quoted in Ah convert to watt-hours the same way.
Pro Tips for Accurate Conversions
Always ask "at what voltage?"
An mAh figure without a voltage is marketing, not a specification.
100 Wh ≈ 27,000 mAh at 3.7 V
The number to remember before flying.
Expect 60–70% real output from a power bank
Voltage boosting and conversion losses eat the rest.
Common Mistakes to Avoid
Comparing mAh across voltages
A 3.7 V and a 12 V pack with the same mAh differ by more than three times in energy.
Convert both to watt-hours first.
Using 5 V instead of cell voltage
Power banks are rated at cell voltage, not USB output voltage.
Use 3.7 V for the rating, then apply a 0.6–0.7 efficiency factor for delivered 5 V charge.
Assuming a bigger battery charges a phone more times
Conversion losses and phone battery size both matter.
Usable Wh ÷ phone battery Wh × 0.85 gives a realistic charge count.
History & Background
Milliamp-hour marketing arrived with mobile phones in the 1990s. Watt-hour labelling became mandatory when aviation authorities needed a consistent way to regulate lithium battery energy in the cabin.
Key Milestones
Sony commercialises lithium-ion, and mAh becomes a consumer specification.
IATA introduces watt-hour thresholds for lithium batteries in air transport.
Airlines tighten rules after cargo incidents, standardising the 100 Wh carry-on limit.
USB-C power delivery pushes manufacturers to publish watt-hour figures alongside mAh.
Global Usage Today
The 100 Wh and 160 Wh thresholds apply worldwide under ICAO rules, which is why watt-hour labelling now appears on nearly every portable battery.
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.