How the calculation works
Wh = mAh × V ÷ 1,000, with V the cell voltage (3.7 V on almost every power bank); carry-on without approval up to 100 Wh, with approval 101–160 Wh
A worked example
A 20,000 mAh power bank at 3.7 V holds 74 Wh (20,000 × 3.7 ÷ 1,000): under 100 Wh, so most airlines let it travel in carry-on baggage without approval. A 27,000 mAh bank holds 99.9 Wh, while 30,000 mAh is 111 Wh and needs the airline's approval.
Why a mAh figure needs its voltage
A milliamp-hour counts charge, not energy. A power bank's mAh is written at its cells' voltage, about 3.7 V, while a phone charges at 5 V or more, so 10,000 mAh at 3.7 V is the same 37 Wh as 7,400 mAh at 5 V. Watt-hours put every battery on one scale, which is why airlines, and this site's prices, use them.
The airline limits
IATA's rules for spare lithium-ion batteries, which most airlines follow: up to 100 Wh travels in carry-on baggage without approval; 101 to 160 Wh needs the airline's approval, usually for two batteries at most; above 160 Wh is not allowed on passenger aircraft. Spare power banks never go in checked baggage. Your airline's own rules win, so check them before you fly.
Common questions
Can I take a 20,000 mAh power bank on a plane?
Usually yes: 20,000 mAh at 3.7 V is 74 Wh, under the 100 Wh limit for carry-on baggage without approval. It must travel in the cabin, not in checked baggage. Check your airline's rules before you fly.
Why does the label also print a smaller rated capacity?
The rated capacity (often about two thirds of the headline figure) is what reaches a device at 5 V after conversion losses. This site never prices it: it compares the headline mAh at 3.7 V, the figure every label states, so every power bank is measured the same way.
What about power stations?
Power stations state their energy in Wh directly, usually far above 160 Wh, so they cannot fly as cabin baggage. This calculator is for power banks; a station's Wh is already on its label.
Method: arithmetic from the label values you enter. Reviewed .