Airlines measure power bank limits in watt-hours (Wh), but most power banks print their capacity in milliamp-hours (mAh). This is one of the most common points of confusion for air travellers. Here is exactly how to convert between them, why the difference matters, and how to use the result to know whether your power bank is allowed on your flight.
The Formula
3.7V is the nominal voltage of a standard lithium-ion cell — the type used in virtually all consumer power banks. Some manufacturers list 3.6V (slightly more conservative) or 3.85V (for higher-energy cells). If your power bank prints a Wh figure directly on the label, use that instead of calculating — it is more accurate than the formula.
Why Airlines Use Wh, Not mAh
Watt-hours measure actual stored energy — the physical capacity to do work. Milliamp-hours measure electric charge, which is voltage-dependent. Two batteries with the same mAh rating but different voltages contain different amounts of energy. A 20,000 mAh battery at 3.7V stores 74 Wh, while a 20,000 mAh battery at 7.4V would store 148 Wh — twice as much energy, and potentially twice as dangerous in a fire scenario.
This is why the IATA standard and the FAA both specify limits in Wh: it is the honest, voltage-independent measure of energy. An mAh limit would not work because voltage varies too much between devices.
Quick Reference Chart
| mAh | Wh (at 3.7V) | Flight status |
|---|---|---|
| 5,000 | 18.5 Wh | Allowed — no approval |
| 10,000 | 37 Wh | Allowed — no approval |
| 15,000 | 55.5 Wh | Allowed — no approval |
| 20,000 | 74 Wh | Allowed — no approval |
| 26,800 | 99.2 Wh | Allowed — no approval |
| 27,000 | 99.9 Wh | Allowed — no approval (borderline) |
| 30,000 | 111 Wh | Needs airline approval |
| 40,000 | 148 Wh | Needs airline approval |
| 43,200 | 159.8 Wh | Needs airline approval (borderline) |
| 50,000+ | 185+ Wh | Not permitted on any flight |
What If My Power Bank Shows Both mAh and Wh?
Use the Wh figure. If there is any discrepancy between the formula result and the printed Wh (common with devices using 3.85V cells), the printed Wh is the number security staff will look at. Keep in mind that some manufacturers slightly round their Wh figures down for marketing purposes — a "74 Wh" device might actually be 74.0 Wh or 73.6 Wh.
Borderline Cases: 27,000 mAh and 43,200 mAh
Two capacity figures sit right at the edge of the 100 Wh and 160 Wh limits:
- 27,000 mAh = 99.9 Wh. Technically under 100 Wh. Most airline agents accept this, but a small number of staff (particularly at Chinese airports) may round to 100 Wh and ask for approval. Carrying documentation of the calculation is wise.
- 43,200 mAh = 159.84 Wh. Technically under 160 Wh. The same borderline risk applies — airlines may treat it as requiring the 100–160 Wh approval process, and some may refuse if they are uncertain.
For devices in these borderline zones, we recommend checking the printed Wh value on the device itself and contacting your airline in advance.
Does the Calculation Change for High-Voltage Power Banks?
A small number of laptops and professional-grade devices use higher-voltage battery packs (7.2V, 7.4V, 11.1V). These are typically not labelled as "power banks" but rather as laptop batteries or portable workstation power supplies. For these, use the actual voltage: Wh = (mAh × actual voltage) ÷ 1,000. These devices often exceed the 100 Wh or 160 Wh limits and require airline approval or are banned entirely.
Sources: IATA Lithium Battery Guidance · FAA Pack Safe · TSA Lithium Batteries