Why airlines use Wh instead of mAh
The number printed largest on a power bank is almost always mAh, but the rules are written in watt-hours. That's because mAh describes charge alone and ignores voltage โ two packs with identical mAh can hold different amounts of energy depending on how their cells are arranged. Fire risk tracks total energy, so the regulation tracks watt-hours.
The conversion is straightforward: Wh = mAh ร V รท 1000. With the usual 3.7 V lithium-ion nominal voltage, a 20,000 mAh pack is about 74 Wh. Where a manufacturer prints the Wh rating directly, use that figure โ it accounts for the actual internal configuration rather than an assumed voltage.
The three thresholds
Under the dangerous goods framework most carriers follow, spare lithium batteries up to 100 Wh can be carried on without any special permission. That covers the overwhelming majority of consumer power banks โ 100 Wh is roughly 27,000 mAh at 3.7 V, which is larger than most people travel with.
Between 100 and 160 Wh you move into approval territory: you need your airline's consent in advance, and you're typically limited to two spares. Above 160 Wh the answer is simply no โ not in the cabin, not in the hold. Large camping and portable-power-station units usually land here, and they need to be shipped as cargo instead.
The mistakes that actually cause problems
Far and away the most common is packing a power bank in a checked bag. It's easy to forget one zipped into a laptop sleeve or a suitcase pocket, and screening will find it. Do a deliberate check before you hand anything over at the desk.
The second is an unreadable label. If the capacity marking has worn off and there's no Wh or mAh figure to verify, staff can refuse the item because they have no way to confirm it's within limits. Travel with units whose markings are still legible, and tape the terminals or bag each one separately so nothing can short against keys or coins.
What this calculator assumes
- Wh = mAh ร V รท 1000, with a 3.7 V default (lithium-ion nominal)
- Up to 100 Wh: carry-on without approval ยท 100โ160 Wh: airline approval, usually max two
- Over 160 Wh: not permitted in cabin or checked baggage
- Spare batteries and power banks are cabin-only everywhere
This page is general guidance, not an official ruling. Requirements differ by carrier and country and have been tightening โ confirm with your airline before departure.