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.

Capacity in mAh

The big number on the box. Tap a common size:

5,000 10,000 20,000 26,800 30,000 40,000

Voltage

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.

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.

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.

Read the full airline rules guide See flight-legal power banks

Quick answers

How do I convert mAh to Wh?

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.