A watt-hour (Wh) measures how much energy a battery stores: one watt of power for one hour. To convert mAh to Wh, multiply the mAh by the battery's voltage and divide by 1,000. A 10,000 mAh power bank at 3.7 V holds 37 Wh. Airlines set battery limits in Wh, with 100 Wh as the main cutoff.
Key facts
- Wh = mAh × V ÷ 1,000 (or Ah × V).
- Use the cell voltage, usually 3.6–3.85 V (3.7 V is the common label), not the 5 V USB output.
- 10,000 mAh = 37 Wh, 20,000 mAh = 74 Wh, 27,000 mAh = 99.9 Wh (all at 3.7 V).
- Airline limits for lithium-ion batteries: up to 100 Wh without approval, 101–160 Wh with airline approval, over 160 Wh forbidden.
- 1 Ah = 1,000 mAh and 1 Wh = 1,000 mWh.
What does mAh mean?
mAh stands for milliamp-hours. It measures electric charge: how much current a battery can deliver over time. A 10,000 mAh battery could, in theory, supply 10,000 milliamps (10 amps) for one hour, or 1,000 milliamps for ten hours.
mAh on its own doesn't tell you how much energy is stored, because it ignores voltage. Two batteries with the same mAh but different voltages hold different amounts of energy. That's why airlines don't use it.
What is Ah?
Ah (amp-hours) is the same unit as mAh, just 1,000 times larger. 1 Ah = 1,000 mAh, so a 5,000 mAh battery is 5 Ah. Larger batteries, such as those for camera rigs and power stations, often list Ah instead of mAh.
What is a watt-hour (Wh)?
A watt-hour is a unit of energy. It combines charge and voltage into one number, so it tells you how much work a battery can actually do. A battery rated 37 Wh could, in theory, supply 37 watts for one hour, or about 18.5 watts for two hours.
Many newer lithium-ion batteries print the Wh rating on the case. If yours does, that's the number to use for flying. You don't need to calculate anything.
What is mWh?
mWh means milliwatt-hours, a thousandth of a watt-hour: 1 Wh = 1,000 mWh. Small batteries, such as those in earbuds or wearables, sometimes list mWh. Divide by 1,000 to get Wh: 37,000 mWh is 37 Wh.
How to convert mAh to Wh
The formula:
Wh = mAh × V ÷ 1,000
Or, if you already have amp-hours: Wh = Ah × V. That's the same calculation the FAA describes.
Worked examples (at 3.7 V)
- 10,000 mAh: 10,000 × 3.7 ÷ 1,000 = 37 Wh
- 20,000 mAh: 20,000 × 3.7 ÷ 1,000 = 74 Wh
- 27,000 mAh: 27,000 × 3.7 ÷ 1,000 = 99.9 Wh, just under the 100 Wh limit
- 30,000 mAh: 30,000 × 3.7 ÷ 1,000 = 111 Wh, which needs airline approval
To skip the arithmetic, use the mAh to Wh converter, or the power bank checker for a verdict with airline rules included.
Why use 3.7 V and not 5 V?
Because the mAh figure describes the battery cells inside, and those cells run at about 3.6–3.85 V. A power bank's USB port puts out 5 V (or more with fast charging), but that's the output after a voltage converter, not the voltage of the stored energy.
Multiplying cell mAh by 5 V overstates the energy. A 20,000 mAh power bank would come out at 100 Wh instead of the correct 74 Wh. Some labels add a smaller "rated capacity" in mAh, measured at the 5 V output after conversion losses. Don't mix the two: use the cell capacity with the cell voltage.
The exact cell voltage matters near the limit. At 3.85 V a 27,000 mAh pack is about 104 Wh, which is over 100 Wh. If the label prints a Wh figure, trust that over your own calculation.
Converting the other way
- Wh to mAh: mAh = Wh × 1,000 ÷ V. So 100 Wh at 3.7 V ≈ 27,027 mAh, which is why about 27,000 mAh is the practical ceiling for a power bank without approval.
- mWh to mAh: mAh = mWh ÷ V. So 37,000 mWh at 3.7 V = 10,000 mAh.
- Ah to Wh: Wh = Ah × V. So a 10 Ah battery at 14.4 V = 144 Wh, which needs airline approval as a spare.
- Wh to Ah: Ah = Wh ÷ V. So 99 Wh at 14.4 V ≈ 6.9 Ah.
mAh to Wh conversion table
Common capacities at the three cell voltages you'll see most often. Verdicts follow the FAA lithium-ion limits and assume one battery or power bank. Airlines may be stricter.
| Capacity | At 3.6 V | At 3.7 V | At 3.85 V | Verdict (at 3.7 V) |
|---|---|---|---|---|
| 5,000 mAh | 18.0 Wh | 18.5 Wh | 19.3 Wh | Allowed, no approval |
| 10,000 mAh | 36.0 Wh | 37.0 Wh | 38.5 Wh | Allowed, no approval |
| 15,000 mAh | 54.0 Wh | 55.5 Wh | 57.8 Wh | Allowed, no approval |
| 20,000 mAh | 72.0 Wh | 74.0 Wh | 77.0 Wh | Allowed, no approval |
| 25,000 mAh | 90.0 Wh | 92.5 Wh | 96.3 Wh | Allowed, no approval |
| 26,800 mAh | 96.5 Wh | 99.2 Wh | 103.2 Wh | Allowed at 3.7 V; check label |
| 27,000 mAh | 97.2 Wh | 99.9 Wh | 104.0 Wh | Allowed at 3.7 V; check label |
| 30,000 mAh | 108.0 Wh | 111.0 Wh | 115.5 Wh | Airline approval needed |
| 40,000 mAh | 144.0 Wh | 148.0 Wh | 154.0 Wh | Airline approval needed |
| 50,000 mAh | 180.0 Wh | 185.0 Wh | 192.5 Wh | Forbidden |
For a page on each size, see the 10,000 mAh, 20,000 mAh and 26,800 mAh power bank pages.
Why do airlines use Wh instead of mAh?
Because Wh measures the energy stored in a battery, which mAh alone can't capture. A mAh figure can't be compared across batteries with different voltages. A 14.4 V camera battery and a 3.7 V phone battery with the same mAh hold very different amounts of energy.
Using Wh gives regulators one scale for every lithium-ion battery, from phones to professional video packs. The FAA, the UK CAA and ICAO all use the same tiers: up to 100 Wh without approval, 101–160 Wh with airline approval, and nothing over 160 Wh. Non-rechargeable lithium-metal batteries are measured differently, by lithium content (2 g per battery).
For what those limits mean in practice, including the 2026 two-power-bank rule, see our guides to power banks on a plane and lithium batteries on planes.
Questions people ask
How many mAh is 100 Wh?
About 27,000 mAh at 3.7 V (100 × 1,000 ÷ 3.7 ≈ 27,027 mAh). At 3.85 V it's about 25,974 mAh, so check the voltage on your label.
How do I calculate watt-hours?
Multiply amp-hours by volts (Wh = Ah × V), or multiply milliamp-hours by volts and divide by 1,000. For example, 20,000 mAh × 3.7 V ÷ 1,000 = 74 Wh.
Is mAh the same as Wh?
No. mAh measures charge and Wh measures energy. You need the voltage to convert one to the other.
Should I use 5 V to convert my power bank's mAh?
No. The mAh on a power bank refers to the internal cells, which are usually 3.6–3.85 V, so use that voltage. Using 5 V overstates the Wh.
What does mAh mean on a battery?
Milliamp-hours: the amount of charge the battery can deliver. Higher mAh means more charge at the same voltage, but you need Wh to compare against airline limits.
