mAh to Wh calculator
Airlines limit power banks by watt-hours, but the case usually prints milliamp-hours. To convert mAh to Wh, multiply the mAh by the voltage (usually 3.6 or 3.7V) and divide by 1,000. Enter a capacity to get the Wh figure and whether you can fly with it.
Last updated September 17, 2026
20,000 mAh at 3.7V
= 74 Wh
At or under the 100Wh limit, so it can go in your carry-on without asking the airline. International rules and many airlines, including American and Delta, limit you to two power banks (Southwest allows one). Never in checked luggage.
If the case prints a Wh figure, go by that: it is what airline staff check. Rules vary by airline (some allow only one power bank), so confirm with yours before you fly.
How to convert mAh to Wh
Watt-hours are volts times amp-hours. Divide the mAh by 1,000 to get amp-hours, then multiply by the voltage:
Wh = mAh × V ÷ 1,000
A 20,000mAh power bank at 3.7V is 20,000 × 3.7 ÷ 1,000 = 74Wh. The calculator rounds up to one decimal place, so the figure it shows never understates a battery.
How to convert Wh to mAh
mAh = Wh × 1,000 ÷ V
At 3.7V, the 100Wh airline limit is 27,027mAh. At 3.6V, it is 27,778mAh.
Why 3.7 volts
Lithium-ion cells have a nominal voltage of about 3.7V, and nearly every power bank is built from them. Many manufacturers rate their cells at 3.6V instead, and a few at 3.85V, which moves the answer by about 3 to 4 percent. If the case prints a Wh figure, use that instead of working it out: it is the number airline staff go by. For what the voltage means on the charging side, see how many watts a USB-C charger needs.
Common power bank sizes in Wh
| Capacity | Wh at 3.6V | Wh at 3.7V | On a plane (at 3.7V) |
|---|---|---|---|
| 5,000 mAh | 18 Wh | 18.5 Wh | Carry-on OK |
| 10,000 mAh | 36 Wh | 37 Wh | Carry-on OK |
| 15,000 mAh | 54 Wh | 55.5 Wh | Carry-on OK |
| 20,000 mAh | 72 Wh | 74 Wh | Carry-on OK |
| 25,000 mAh | 90 Wh | 92.5 Wh | Carry-on OK |
| 26,800 mAh | 96.5 Wh | 99.2 Wh | Carry-on OK |
| 27,000 mAh | 97.2 Wh | 99.9 Wh | Carry-on OK |
| 30,000 mAh | 108 Wh | 111 Wh | Over 100Wh: often refused |
| 40,000 mAh | 144 Wh | 148 Wh | Over 100Wh: often refused |
| 50,000 mAh | 180 Wh | 185 Wh | Not allowed in baggage |
| 60,000 mAh | 216 Wh | 222 Wh | Not allowed in baggage |
The airline rules for power banks
Up to 100Wh: carry-on, no approval needed. That covers almost every power bank up to about 26,800mAh. International rules and many airlines allow two per passenger, and Southwest allows one.
Over 100Wh, up to 160Wh:often refused. International rules still allow power banks this size with the airline’s approval, but IATA’s 2026 guidance advises airlines not to accept them, and American, Delta and Southwest cap power banks at 100Wh. Spare camera and drone batteries this size can still fly with the airline’s approval, so ask before your travel day, not at the gate.
Over 160Wh: not allowed in passenger baggage; batteries this size ship as cargo. Most camping power stations are in this group.
Never in checked luggage, whatever the size. There is more on the 2026 rule changes in our guide to whether you can bring a power bank on a plane.
Power banks under the 100Wh limit
Every power bank on this shortlist is well under the line by its listed capacity. Prices change often, so check the current one on Amazon.
What we would buy (5)
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- Check price on Amazon
Anker621 MagGo magnetic power bank, 5,000mAh
Opens Amazon in a new tab.About 18 to 19Wh, a fraction of the limit. A magnetic top-up for a phone rather than a full day's charge.
- Check price on Amazon
Anker633 magnetic power bank with stand, 10,000mAh
Opens Amazon in a new tab.About 36 to 37Wh. Snaps onto a MagSafe iPhone and folds out into a stand.
- Check price on Amazon
AnkerNano 3-in-1 travel power bank, 10,000mAh
Opens Amazon in a new tab.About 36 to 37Wh and 30W, with a built-in USB-C cable and a fold-out wall plug, so it is also your charger.
- Check price on Amazon
UGREENNexode 20,000mAh 45W power bank
Opens Amazon in a new tab.About 72 to 74Wh, comfortably inside the limit, with a built-in cable and enough output for a tablet or a small laptop.
- Check price on Amazon
UGREENNexode 20,000mAh 130W power bank
Opens Amazon in a new tab.Listed at 72Wh, with 130W of output for a laptop. The most powerful here, and still well under the line.
No prices or star ratings here. Prices change daily and we do not track them, so Amazon shows you the current one. Nothing on this list has been tested.
Common questions
How do you convert mAh to Wh?
Multiply the mAh by the cell voltage and divide by 1,000. Most power banks are rated at 3.6 or 3.7V, so a 20,000mAh bank at 3.7V is 20,000 × 3.7 ÷ 1,000 = 74Wh.
How many Wh is a 10,000mAh power bank?
About 37Wh at 3.7V, or 36Wh at 3.6V. Either way it is well under the 100Wh carry-on limit.
How many Wh is a 20,000mAh power bank?
About 74Wh at 3.7V, or 72Wh if its cells are rated at 3.6V. Either way it is under the 100Wh limit and fine in a carry-on.
How many Wh is a 26,800mAh power bank?
About 96.5Wh at 3.6V, the voltage most banks of this size are rated at, or 99.2Wh at 3.7V. Both are under the 100Wh limit.
What is 100Wh in mAh?
About 27,000mAh at 3.7V, or about 27,800mAh at 3.6V. That is why so many travel power banks stop at about 26,800mAh.
Can I take a 30,000mAh power bank on a plane?
Often not. At 3.7V it is 111Wh (108Wh at 3.6V), over the 100Wh line. American, Delta and Southwest do not accept power banks over 100Wh, and IATA's 2026 guidance advises airlines not to. A 26,800mAh bank avoids the problem.