Power bank capacity calculator
What does 20,000 mAh really hold, how many times will it fill your phone, and can it come on the plane? Read the label and find out.
Capacity
74 Wh
20,000 mAh × 3.7 V ÷ 1000
- Usable at 85%
- 62.9 Wh
- Delivered at 5 V
- 12,580 mAh
- Device charges
- ≈ 4.1
Within 100 Wh. FAA and IATA rules allow it as a spare in carry-on baggage, without airline approval. Spare power banks must never go in checked baggage. Airlines can set stricter limits, including how many power banks you carry and whether you may use them on board: check with your airline before you fly.
At 3.7 V, the largest bank within 100 Wh is 27,027 mAh, and within 160 Wh 43,243 mAh.
General FAA and IATA limits. Airlines can be stricter: check with your airline before you fly.
From mAh to watt-hours
Power banks are sold by milliamp-hours, but mAh alone is not an amount of energy: it has to be multiplied by the voltage of the cells inside, usually 3.6 or 3.7 V, printed on the label as the nominal or rated voltage. Many labels print the Wh figure too; if yours does, use it.
Wh = mAh × cell voltage ÷ 1,000
Charges ≈ Wh × efficiency ÷ device battery Wh
Your phone does not get all of it. The bank raises the voltage to 5 V or more for USB, and some energy is lost as heat on the way, so the efficiency box starts at an estimated 85%. Phone batteries are rated the same way: mAh times their own voltage.
For flights, FAA and IATA rules let you carry spare power banks of up to 100 Wh in carry-on baggage. Over 100 and up to 160 Wh needs the airline's approval, with at most two spares; over 160 Wh cannot go in passenger baggage at all.
Sources
- Federal Aviation Administration, PackSafe: Lithium Batteries: spare lithium batteries and power banks in carry-on baggage only; up to 100 Wh per battery; up to two spares of 101–160 Wh with airline approval; airlines may be stricter.
- IATA, Passengers travelling with lithium batteries: spares over 100 Wh up to 160 Wh need operator approval (two at most); over 160 Wh only as cargo under the Dangerous Goods Regulations.
Questions
Why don't I get the full mAh into my phone?
The mAh is counted at the cell voltage, about 3.7 V, while USB delivers 5 V or more, and some energy turns into heat. The figure delivered at 5 V is therefore lower, as the result shows.
Can a power bank go in my checked bag?
No. FAA and IATA rules keep spare lithium batteries, power banks included, in carry-on baggage. If your cabin bag is checked at the gate, take the power bank out first.
Are the limits per bank or per passenger?
The Wh limits apply to each battery. Numbers are limited too: at most two spares over 100 Wh, and airlines can set their own limits on how many you carry.