mAh to Wh Calculator: Is Your Power Bank Flight Legal?
mAh to Wh calculator
Convert mAh to Wh in one step. Enter your power bank’s printed capacity and we turn it into watt hours, the figure airlines actually use, then tell you whether it flies. The rule is the same across the UK, EU and US: under 100 watt-hours needs no approval, 100 to 160Wh needs airline permission, and over 160Wh is banned from passenger aircraft.
The big number on the box. Tap a common size:
5,00010,00020,00026,80030,00040,000
Leave at 3.7V unless your bank states otherwise. This is the figure airlines use.
Enter a capacity
We will work out the watt-hours and tell you if it flies
If your bank prints a Wh figure on the casing, that printed number is what security goes by.
100Wh is about 27,000mAh. 160Wh is about 43,000mAh. Most consumer banks are well under the line.
Under 100Wh flies with no approval. The mAh to Wh calculator gives you the verdict in one step.
How to convert mAh to Wh
Divide the mAh by 1,000, then multiply by 3.7. That is the whole formula: Wh = (mAh / 1,000) x 3.7. A 20,000mAh power bank works out to 20 x 3.7 = 74Wh, comfortably under the flight limit.
Why 3.7 volts? It is the nominal voltage of the lithium-ion cells inside every power bank, and the figure regulators and airlines assume when they set the 100Wh limit.
Going the other way? Wh to mAh is the reverse: multiply the Wh by 1,000, then divide by 3.7. The 100Wh airline limit works out to about 27,000mAh.
Printed Wh wins. If your bank already shows a Wh figure on the casing, security goes by that printed number, not your arithmetic.
Why your phone gets less than the printed mAh. The mAh rating is measured at the cell’s own 3.7V, but the bank has to step up to 5V or more to charge a device, and some energy is lost as heat along the way. As a rule of thumb, expect roughly two thirds of the printed capacity to reach your phone. Our iPhone charges calculator does that per-model maths for you.
Whatever your bank’s size, six rules still apply
Hand luggage only. Power banks are banned from checked bags on every airline, worldwide.
Two banks maximum under the global baseline since 27 March 2026. Wizz Air, Emirates and Southwest allow only one.
Keep it within reach, on you, in the seat pocket or under the seat. Not in the overhead locker.
Do not recharge the bank on board, and on many airlines do not use it to charge devices either.
The rating must be readable. A worn or missing label is grounds for confiscation.
Never fly with a swollen or damaged bank. Recycle it before the trip, not after.
Common sizes at a glance
Worked out at the 3.7V nominal voltage airlines assume.
Printed capacity
Watt-hours
Status
5,000mAh
18.5Wh
Allowed
10,000mAh
37Wh
Allowed
20,000mAh
74Wh
Allowed
26,800mAh
99.2Wh
Allowed, just under
30,000mAh
111Wh
Approval needed
40,000mAh
148Wh
Approval needed
50,000mAh
185Wh
Banned
Formula and bands per the ICAO and IATA framework that the UK CAA, EASA and US FAA all implement: Wh = mAh divided by 1,000, multiplied by 3.7. Airline policy on counts and in-flight use varies on top.
Why airlines measure in watt hours, not mAh
A mAh figure only describes a battery at one particular voltage, so the same printed number can mean different amounts of stored energy in different devices. Watt hours measure the energy itself, which is what matters when a lithium battery is sitting in a cabin at 35,000 feet. So the IATA battery guidance, the UK CAA and the US FAA all write their limits in Wh, while power bank boxes shout the bigger mAh number. Our mAh to Wh calculator exists to bridge exactly that gap: type in the marketing number, get back the regulatory one.
Divide the mAh by 1,000, then multiply by 3.7, the nominal voltage of lithium-ion cells. A 25,000mAh bank is 25 times 3.7, which is 92.5Wh. If a Wh figure is already printed on the casing, that number wins.
What is the biggest power bank I can fly with?
Without approval, 100Wh, which is about 27,000mAh. That is why so many travel banks cluster at 20,000 to 27,000mAh: it is the largest size that clears security with no paperwork in the UK, EU and US.
Is a 20,000mAh power bank allowed on a plane?
Yes. At 3.7V it works out to 74Wh, comfortably under the 100Wh limit, with no approval needed on any airline in the UK, EU or US.
Can I take a 30,000mAh power bank on a plane?
Only with advance airline approval. 30,000mAh is about 111Wh, in the 100 to 160Wh band, and several carriers including Ryanair and Wizz Air refuse power banks above 100Wh entirely.
How many mAh is 100Wh?
About 27,000mAh at the 3.7V nominal voltage airlines assume, and the 160Wh approval ceiling works out to about 43,000mAh. That maths is the reason 26,800mAh became the classic travel size: it is the biggest round number that clears the no-approval limit.
Is a 40,000mAh power bank allowed on a plane?
Only with advance airline approval. 40,000mAh converts to about 148Wh, which sits in the 100 to 160Wh permission band, and several carriers including Ryanair and Wizz Air refuse power banks above 100Wh entirely. For regular flying, stay at 27,000mAh or below.
What voltage should I use in the mAh to Wh calculator?
Leave it at 3.7V. That is the nominal voltage of the lithium-ion cells inside a power bank and the figure regulators use to set the flight limits. Only change it if your bank’s label states a different nominal voltage, and if the label already prints a Wh figure, that printed number is what security goes by.
