Most travellers check the mAh number when buying a power bank. Airlines check the Wh number when you board. Here is why that difference matters — and how to make sure your device clears security.
Two Numbers, One Device
Every power bank has two capacity numbers. The first is mAh — milliampere-hours — which appears on almost every product listing, box and device label. The second is Wh — watt-hours — which is what airlines, security officers and international aviation regulations actually use to determine whether your device is allowed on a flight.
Most travellers know their power bank's mAh number. Very few know its Wh value. This gap is exactly where confiscations happen.
What mAh Actually Measures
mAh measures electrical charge — specifically, how much current a battery can deliver over time. A 10,000 mAh battery can theoretically deliver 10,000 milliamps for one hour, or 1,000 milliamps for ten hours.
The problem with mAh as a safety measurement is that it tells you nothing about voltage — and voltage is what determines how much energy is actually stored. Two batteries with identical mAh ratings but different voltages contain completely different amounts of energy. A 10,000 mAh phone battery at 3.7V stores far less energy than a 10,000 mAh laptop battery at 7.4V.
This is why airlines do not use mAh. It is an incomplete measurement for safety purposes.
What Wh Actually Measures
Wh measures energy — the product of voltage and charge over time. It tells you exactly how much energy is stored in a battery, regardless of voltage. This is the number that matters for aviation safety because it directly relates to how much heat a battery can produce if it fails.
The ICAO 100 Wh carry-on limit is a Wh limit, not a mAh limit. When a security officer checks your power bank, they are looking for the Wh rating — either printed on the device, on the packaging, or calculated from the specifications.
How to Convert mAh to Wh
The formula is straightforward:
Wh = mAh × V ÷ 1,000
For most consumer power banks, the nominal voltage of the lithium-ion cells inside is 3.7V. This means the calculation for common power bank sizes looks like this:
- 5,000 mAh: 5,000 × 3.7 ÷ 1,000 = 18.5 Wh ✓
- 10,000 mAh: 10,000 × 3.7 ÷ 1,000 = 37 Wh ✓
- 20,000 mAh: 20,000 × 3.7 ÷ 1,000 = 74 Wh ✓
- 26,800 mAh: 26,800 × 3.7 ÷ 1,000 = 99.2 Wh ✓ (just under the limit)
- 27,000 mAh: 27,000 × 3.7 ÷ 1,000 = 99.9 Wh ✓ (borderline)
- 30,000 mAh: 30,000 × 3.7 ÷ 1,000 = 111 Wh ⚠ (requires airline approval)
- 43,000 mAh: 43,000 × 3.7 ÷ 1,000 = 159.1 Wh ⚠ (maximum with approval)
Use our free mAh to Wh calculator to check your specific device instantly — no maths required.
Why the 3.7V Figure Is Not Always Accurate
3.7V is the nominal voltage of a single lithium-ion cell. Most consumer power banks use 3.7V cells, which makes this the standard conversion factor. However, some high-capacity power banks use 3.6V cells, and some specialist devices use higher voltages.
If your power bank's specifications list a different voltage, use that number instead of 3.7V. The formula remains the same — only the voltage figure changes.
When in doubt, check the device label or manufacturer specifications for the rated voltage. If no voltage is listed and you cannot find specifications, the 3.7V default is a safe and widely accepted assumption for standard consumer power banks.
The 100 Wh Limit Explained
The ICAO 100 Wh carry-on limit has been in place for years but is now enforced more strictly than ever. Under ICAO 2026 rules — binding across 193 countries — the limits are:
- Under 100 Wh: Permitted on all flights without restrictions or approval
- 100–160 Wh: Permitted with prior airline approval, maximum two devices per passenger
- Over 160 Wh: Prohibited entirely — carry-on and checked baggage
A 20,000 mAh power bank at 3.7V equals approximately 74 Wh — comfortably within the universal limit. This is why all three NOBOARDER power banks are designed to stay under 100 Wh.
What Happens If Your Device Has No Wh Label
This is increasingly a problem at airports in Japan, Australia and several EU hubs. Security officers are instructed to check for a readable Wh rating on the device itself or its packaging. If no Wh label exists and the officer cannot verify the capacity, they have the authority to refuse the device.
Some officers will perform the mAh-to-Wh conversion on the spot. Many will not. If your power bank has only a mAh rating and no Wh label, you are relying on the individual officer's willingness to do the calculation — and not all of them will.
All NOBOARDER power banks have the Wh rating permanently printed on the device. No calculations required at the gate.
How Many Charges Will You Actually Get?
mAh is useful for one thing: estimating how many times a power bank will charge your devices. The calculation accounts for the fact that real-world charging is never 100% efficient — typically around 80% due to heat loss and conversion losses.
Estimated charges = (Power bank mAh × 0.8) ÷ Device battery mAh
For common devices:
- iPhone 15 Pro (3,274 mAh) from a 10,000 mAh bank: approximately 2.4 full charges
- Samsung Galaxy S24 (4,000 mAh) from a 10,000 mAh bank: approximately 2.0 full charges
- iPad Air (7,606 mAh) from a 20,000 mAh bank: approximately 2.1 full charges
- MacBook Air M2 (52,600 mAh) from a 20,000 mAh bank: approximately 0.3 full charges
Use our interactive calculator to check your specific devices — select your power bank capacity, choose your devices, and see exactly how many charges you will get.
The Simple Rule to Remember
If your power bank is under 20,000 mAh and uses standard 3.7V lithium-ion cells, it is almost certainly under 100 Wh and will clear security on any flight in the world without question — provided it also carries the right certifications for your destination.
The certifications that matter are CCC for China, CE for Europe, FCC for North America, and UN38.3 for all international air transport. The Wh calculation tells you whether the energy level is acceptable. The certifications tell security that the battery has been tested and verified as safe.
Both matter. Neither alone is sufficient for global travel.
All NOBOARDER power banks are under 100 Wh and carry full CCC, CE, FCC, UN38.3 and RoHS certification. Browse our certified power banks or check your current device with our free Wh calculator.
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