mAh ↔ Wh converter
Enter the capacity in any unit and the battery's nominal voltage from its label. All values are worked out in your browser.
Only want to know how long a charge lasts? Use the battery life calculator.
How to use the converter
- Enter the capacity you have, for example 4,000 from a battery listing, or 53,015 from your battery report.
- Pick its unit. Battery reports use mWh; shops and battery labels often use mAh or Wh.
- Enter the voltage printed on the battery or in its specifications. If you only know the number of cells, use one of the common values as a rough guide.
- Press Convert to see the capacity in mAh, Wh and mWh, plus where it sits against the usual airline limits.
The formula
- Wh = mAh × V ÷ 1,000 (or Ah × V). 4,000 mAh × 11.55 V = 46,200 mWh = 46.2 Wh.
- mAh = Wh × 1,000 ÷ V. 50 Wh at 11.55 V = 4,329 mAh.
- mWh = Wh × 1,000. 53,015 mWh in a battery report is 53.015 Wh.
Milliamp-hours measure charge; watt-hours measure energy. The same 50 Wh battery is about 4,329 mAh if it runs at 11.55 V but about 3,247 mAh at 15.4 V. That is why a bigger mAh figure does not always mean a bigger battery.
Where to find the voltage
Look for a line such as 11.55V or 15.4V ⎓ on the battery label, the replacement listing or the laptop's specifications. Lithium-ion laptop packs usually combine 2, 3 or 4 cells in series, which is why voltages cluster around these values:
| Cells in series | Typical nominal voltage |
|---|---|
| 2 cells | 7.2–7.7 V |
| 3 cells | 10.8–11.55 V |
| 4 cells | 14.4–15.4 V |
The Windows battery report does not show the voltage, so you need the label or the specifications for an exact mAh figure.
Real examples from our battery reports
These capacities come from real Windows battery reports in our real battery report data. The reports give mWh only, so the mAh figures below show what the same energy would be at two common voltages.
| Laptop (design capacity) | Wh | At 11.55 V | At 15.4 V |
|---|---|---|---|
| Sister's Lenovo (45,000 mWh) | 45.0 Wh | 3,896 mAh | 2,922 mAh |
| Brother's HP ZBook (53,015 mWh) | 53.0 Wh | 4,590 mAh | 3,443 mAh |
| Home ThinkPad (99,470 mWh) | 99.5 Wh | 8,612 mAh | 6,459 mAh |
The home ThinkPad's battery is rated 99.47 Wh, just under the 100 Wh line that airlines use. Large laptop batteries are often sized just below that limit for this reason.
The 100 Wh airline limit
The US Federal Aviation Administration limits rechargeable lithium-ion batteries carried by passengers to 100 Wh per battery. With airline approval, passengers may carry up to two spare batteries of 101–160 Wh. Spare batteries and power banks must travel in carry-on baggage, with the terminals protected from short circuits. To work out the rating, the FAA says to multiply the voltage by the amp-hours, which is exactly what this converter does.
Rules differ by country and airline, so check with your carrier before you fly with a large spare battery.
Common mistakes
- Comparing mAh across different voltages. A 6,000 mAh pack at 7.7 V holds less energy (46.2 Wh) than a 4,000 mAh pack at 15.4 V (61.6 Wh).
- Using a phone battery voltage. Power banks and phone batteries are often rated at 3.6–3.85 V per cell. Applying that to a laptop pack gives a figure three or four times too high.
- Mixing mWh and mAh in the health formula. Battery health is Full Charge Capacity ÷ Design Capacity, both in the same unit. See the battery health percentage guide.
- Trusting a listing with no voltage. A replacement listed only in mAh can't be compared fairly with your original battery. Ask the seller for the voltage or the Wh rating.
Frequently asked questions
How do I convert mAh to Wh?
Multiply mAh by the battery's voltage and divide by 1,000. A 5,000 mAh battery at 15.4 V is 5,000 × 15.4 ÷ 1,000 = 77 Wh.
How many mAh is a 50 Wh laptop battery?
It depends on the voltage: about 4,329 mAh at 11.55 V, 4,505 mAh at 11.1 V, or 3,247 mAh at 15.4 V.
Why does my Windows battery report show mWh instead of mAh?
Windows reports energy in milliwatt-hours, a unit that already includes the voltage. Divide by 1,000 to get Wh, then use the converter if you need mAh.
Is Wh or mAh better for comparing laptop batteries?
Wh, because it already includes the voltage. Two batteries with the same Wh rating hold the same energy, whatever their mAh figures say.
Can I take a 99 Wh laptop battery on a plane?
Under FAA guidance, lithium-ion batteries up to 100 Wh are within the standard passenger limit, but individual airlines can set stricter rules, so check with yours.
How this tool was verified
The conversion is the FAA's own method, watt-hours = volts × amp-hours, described on its PackSafe lithium batteries page, which is also the source of the 100 Wh and 160 Wh limits above. I checked the results against the mWh values in four real Windows battery reports generated between 3 and 7 November 2026. Values are calculated in your browser and are not uploaded or stored.
Senior software engineer in Karachi with more than five years of experience building web applications in ASP.NET Core, C# and JavaScript. He built the free battery health checker and these calculators, and checks them against Microsoft and laptop makers’ documentation and real battery reports.