How to correctly convert mAh to Wh for a power bank to avoid mistakes when checking at the airport?

This is one of the most common and dangerous questions because a conversion error can cost you your power bank. Airlines check capacity in watt-hours (Wh), while power banks usually have milliamp-hours (mAh) written large on the case. Simply removing three zeros to get watt-hours is a gross mistake! For example, 20,000 mAh is not 20 Wh, but a whole 74 Wh.

Here is a simple and accurate conversion formula:

For most standard power banks, the voltage of one cell is 3.7 V. Let's calculate with popular examples:

• 10,000 mAh → (10,000 × 3.7) / 1000 = 37 Wh (no problem)
• 20,000 mAh → (20,000 × 3.7) / 1000 = 74 Wh (also allowed)
• 27,000 mAh → (27,000 × 3.7) / 1000 = 99.9 Wh (almost the limit, but still allowed)
• 30,000 mAh → (30,000 × 3.7) / 1000 = 111 Wh (requires airline permission)

Where to find the voltage? Look for small text on the power bank case. There should be a line like "20000 mAh / 3.7 V / 74 Wh". If the marking is worn off, bring the box or a printout from the manufacturer's website. Without capacity confirmation, the device may not be allowed on board.

We covered all the details in the article: Which power bank can be taken on a plane: complete instructions to avoid confiscation

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