mAh to Wh: the same number is not the same battery
The conversion takes one line. The number that makes it work is the voltage, and it is the number most listings do not give you.
In short
- The conversion
- Wh = (mAh ÷ 1,000) × V. That is the whole formula. It is a definition, not a measurement, and it is the same on every calculator site.
- Why it is not the answer
- Because mAh is charge and Wh is energy, and the voltage is what converts one into the other. The same 5,200 mAh is 74.9 Wh at 14.4 V and 56.2 Wh at 10.8 V — a third less energy behind an identical-looking label.
- The limit that matters
- Aviation rules are written in Wh, not mAh: 100 Wh or less per battery in carry-on, and 100–160 Wh only with airline approval. A power bank sold in mAh has to be converted before you know which side of that line it is on.
- What 100 Wh is in mAh
- It depends entirely on the voltage: 27,027 mAh at 3.7 V, 20,000 mAh at 5 V, 6,944 mAh at 14.4 V. There is no single answer, which is why the question keeps getting asked.
Convert it
Two boxes. Put the charge in one and the voltage in the other. The voltages underneath are the ones batteries are actually rated at — pick the one your label uses.
— watt hours
The same mAh, two different batteries
This is the part the calculator sites leave out. A charge figure on its own does not describe a battery, because the energy it holds is that charge multiplied by a voltage that varies by chemistry and by how the pack is wired.
A robot vacuum battery is the clearest published example, and both figures below come from the same specification sheet:
| Label on the pack | Voltage | Energy it actually holds |
|---|---|---|
| 5,200 mAh | 10.8 V | 56.2 Wh |
| 5,200 mAh | 14.4 V | 74.9 Wh |
The 5,200 mAh and both voltages are the maker’s; converting them to watt hours is our arithmetic, and it is the same one-line formula in each row.
The same trap runs the other way too: a pack advertised as the higher number is not necessarily the bigger battery. If the voltage is lower, the energy can be lower while the mAh figure is identical.
What 100 Wh is in mAh
This is the most-asked form of the question, because aviation rules are written in watt hours and power banks are sold in milliamp hours. The FAA states the limit as 100 Wh per battery, with 100–160 Wh allowed only with airline approval. So the conversion is the whole of the compliance question.
| If the rating is quoted at | 100 Wh is |
|---|---|
| 3.7 V | 27,027 mAh |
| 5 V | 20,000 mAh |
| 10.8 V | 9,259 mAh |
| 14.4 V | 6,944 mAh |
The voltages are ours to choose and the division is ours; the 100 Wh limit is the FAA’s. Rearranging the formula gives mAh = (Wh ÷ V) × 1,000.
Which means a 20,000 mAh power bank is exactly on the limit if its figure is quoted at 5 V, and comfortably inside it if the same figure is quoted at 3.7 V. Same number on the case, two different answers at the airport.
What to check before you trust a number
- Find the voltage, not the mAh. If a listing gives milliamp hours and no voltage, the energy figure cannot be worked out and the aviation question cannot be answered. That is a gap in the listing, not in the arithmetic.
- Ask which voltage the figure is quoted at. A pack can be described by the charge its cells hold or by the energy it delivers, and those are quoted at different voltages. The maker is the only one who can settle it.
- Convert before you fly, not at the gate. The rule is a watt-hour rule, so the number that decides it is the one you get from this page, not the one printed on the case.
Where this comes from
This page rests on one published specification and one published rule, plus arithmetic. No battery was bought, charged, discharged or measured, and nothing here is a test result.
- That lithium-ion batteries carried by airline passengers are limited to a rating of 100 watt hours per battery, with higher ratings requiring airline approval: the US Federal Aviation Administration’s passenger battery guidance, read on 7 October 2026.
- The same limit stated for security screening, with the over-100 Wh category set out separately: the US Transportation Security Administration’s “what can I bring” entries on lithium batteries, read on 7 October 2026.
- That the same pack is rated 5,200 mAh at both 10.8 V and 14.4 V: the manufacturer specification quoted on our own robot vacuum battery page, which names the source it was read from.
- That Wh = (mAh ÷ 1,000) × V: the definition of the two units. It is not a finding, and it is not ours.
Every figure on this page is either a published number with its source named above, or a division we have labelled as ours. Nothing here is estimated, and no number has been filled in where a source was not available.