How to Convert mAh to Wh for a Power Bank
How to convert mAh to Wh for a power bank, with examples from real listings and why the watt-hour rating matters for flying.
By GadgetsDiary Editorial Team
Updated November 12, 2026
Safety: Power banks contain lithium-ion cells. Use the cables the manufacturer supplies or recommends, keep the unit away from heat, never use a damaged or swollen battery, and follow the manual. This guide is general information, not a substitute for the manufacturer instructions or your airline policy.
Power bank listings show capacity in milliamp-hours, but airlines and laptop batteries use watt-hours. Converting between them tells you whether a bank is under an airline limit and how it compares with your laptop battery.
The Formula
Watt-hours equal volts multiplied by amp-hours. The FAA gives the same method: multiply the battery voltage by the amp-hours. To turn milliamp-hours into amp-hours, divide by 1,000. The voltage is the nominal voltage of the battery cells, which is often printed on the unit label.
Because cell voltage varies, there is no single conversion factor for every bank. When a listing states the Wh rating, use that number.
Examples From Listings
Manufacturers often print both numbers. The listings we reviewed give 72.36Wh for 20,100mAh, 99.75Wh for 26,250mAh, 73Wh for 20,000mAh and 99.9Wh for 27,000mAh. The ratios differ slightly between brands, which is why the Wh figure on the unit is the one to trust.
| Listed capacity | Listed watt-hours |
|---|---|
| 20,100mAh | 72.36Wh |
| 20,000mAh | 73Wh |
| 26,250mAh | 99.75Wh |
| 27,000mAh | 99.9Wh |
Why It Matters for Flying
Airlines set limits by watt-hour rating, not by milliamp-hours. The FAA page PackSafe describes the tiers, and our flying guide summarizes them. Always check the Wh printed on the bank and your airline policy.
Why It Matters for Laptops
Laptop batteries are rated in watt-hours too, so comparing the bank Wh with your laptop battery Wh shows how much reserve the bank holds. Conversion losses mean a bank delivers less than its rated figure to a device, so treat the comparison as a rough guide only.
Frequently Asked Questions
Is mAh enough to compare power banks?
Only when the voltage matches. Watt-hours are a fairer comparison across brands, so use Wh when the listing gives it.
Where is the Wh printed?
Usually on the label of the power bank, and sometimes on the listing. If it is missing, use volts multiplied by amp-hours.
Does a higher mAh always mean a higher Wh?
Generally yes within a brand, but different cell voltages can make the ratio differ, so check the Wh figure.
Related Guides
Explore more in our Travel and Airline Power Banks category, the Power Banks hub and our guide on how to choose a travel power bank.
About the author
The GadgetsDiary editorial team compares portable power and charging products using manufacturer specifications and Amazon listing data. Read how we choose and rank products on our How We Review and Editorial Policy pages.