Tool
Power bank calculator: mAh to Wh, airline limits, and how many charges
A power bank's mAh number alone does not tell you whether it can fly or how far it gets a laptop. Enter the capacity on the label and see both.
ormAh
Cell voltage(3.7V if the label does not say)
Energy
74.0 Wh
20,000 mAh × 3.7V ÷ 1000. About 0.9–1 full charges of a 13" laptop (~50Wh battery), after the 30–40% lost to conversion.
Flying in the US
OK in carry-on
At or under 100Wh, US rules allow it in your carry-on with no airline approval. Never in checked bags.
Capacity is half of it for a laptop. To charge while you work, the bank's USB-C output must match the wattage on your laptop's charger; a 30W bank on a 65W laptop only slows the drain. Work out the wattage you need.
Power banks we have reviewed that fit in carry-on
JUOVI 65W 20000mAh USB-C Laptop Power Bank≈74Wh · 65W out · laptop-capable
Anker 20,000mAh 30W Portable Charger with USB-C and Lightning Cables≈74Wh · 30W out- TESSAN 10000mAh 30W Portable Charger with Built-In USB-C Cable≈37Wh · 30W out
- Anker Nano 3-in-1 Portable Charger (10,000mAh, 30W)≈37Wh · 30W out
- Selore&S-Global 3-in-1 10000mAh Portable Charger≈37Wh
Questions this answers
How do I convert mAh to Wh?
Multiply mAh by the cell voltage and divide by 1,000. Power banks rate mAh at the cell's nominal 3.6 or 3.7V, so 20,000mAh is 72–74Wh. If the label prints a Wh figure, use that.
Can I bring a power bank on a plane?
In the US, yes — in your carry-on only, never in checked bags. Up to 100Wh needs no approval. From 101 to 160Wh you need the airline's approval and may carry two at most. Above 160Wh is not allowed on passenger flights. Some airlines add their own rules, such as no charging in flight, so check before you fly.
Is a 26,800mAh power bank under 100Wh?
Usually: 26,800mAh is 96.5Wh at 3.6V and 99.2Wh at 3.7V, both under the limit. Banks sold as 27,650mAh land at 99.5Wh (3.6V) or 102.3Wh (3.7V), so read the Wh on the label.
Why does my power bank give fewer charges than its capacity suggests?
Energy is lost raising the cell's 3.7V to 5–20V and again inside the device as it charges. Expect roughly 60–70% of the rated Wh to reach the battery.
The flight rules are the US FAA's for spare lithium-ion batteries; airlines and other countries can be stricter. Charge counts are estimates from the rated energy, not measurements. The power banks listed are reviews on this site, with Wh worked out from the mAh in their listing at 3.7V. See also the charger calculator.