Power banks are sold in mAh, and airlines set their limits in watt-hours, so the number on the box does not answer the question at the gate. Converting mAh to Wh takes one division and one multiplication, and the only figure you can get wrong is the voltage.
Put in the mAh and the voltage printed beside it on the label. This mAh to Wh converter works out the watt-hours, where they sit against the 100 Wh and 160 Wh lines the FAA and IATA set for lithium-ion batteries, and the largest capacity that fits under each at your voltage. Every figure it supplies names its source, and the list of what it cannot tell you is below the answer.
In this guide
The mAh to Wh converter
The mAh figure on the battery or power bank's label, such as 10000mAh or 20,000 mAh.
The voltage printed beside the mAh on the label: usually 3.6, 3.7 or 3.85 V for a lithium-ion power bank or phone battery. Not the 5 V of its USB port. A laptop battery is often 11.1 to 15.4 V.
How that is worked out, line by line
- Capacity in amp-hours10.00 Ah
- Share of the 100 Wh carry-on line %
- The same capacity counted at 3.6 V36.0 Wh
- Largest capacity within 100 Wh at this voltage27,027 mAh
- Largest capacity within 160 Wh at this voltage43,243 mAh
On those numbers you are in the 100 Wh or less: no airline approval needed band, which is the section below.
This runs entirely inside your browser. Nothing you type is sent anywhere, saved or read by this site, and the page keeps working with the network unplugged.
Newsletter
One email a week, and only when there is something in it
Every guide I published or rewrote that week, up to six of them, each with a line on who it is for and what it settles. No prices, no deals, nothing else.
It goes out on Thursday mornings. In a week when nothing new went up, nothing is sent.
Your address goes to MailerLite, who deliver the email, and nowhere else. Every email has an unsubscribe link. The email ends with one link to my Amazon storefront, and as an Amazon Associate I earn from qualifying purchases. Privacy policy.
Where every number here comes from
No part of this was measured on a bench here. This site works from published specifications and from what owners report, and every number below is either one you typed in or a published figure with its source named next to it.
The figures this page supplies
- Milliamp-hours in an amp-hour: 1,000. The SI prefix milli is one thousandth (NIST), and the FAA and IATA both say to divide a battery's mAh by 1000 to get its Ah before multiplying by the voltage.
- Largest lithium-ion battery an airline takes without approval: 100 Wh. The FAA's PackSafe rules for lithium batteries and IATA's Dangerous Goods Regulations (Table 2.3.A): up to 100 Wh per battery, no airline approval needed.
- Largest lithium-ion battery an airline may approve: 160 Wh. The same FAA and IATA rules: over 100 and up to 160 Wh needs the airline's approval, with at most two spares per person; over 160 Wh is not allowed in passenger baggage.
- Nominal voltage of a standard lithium-ion cell: 3.6000 V. Battery University (BU-303, Confusion with Voltages): most lithium-ion systems keep to a nominal 3.60 V a cell, and the 3.70 V some labels print is a higher, mostly marketing figure.
Why each step is the step it is
- Capacity in amp-hours:
mah / mah_per_ah. mAh divided by 1000, the first step the FAA and IATA give. - Energy in watt-hours:
ah * volts. Amp-hours times volts, the formula the FAA and IATA both publish: Wh = V x Ah. - Share of the 100 Wh carry-on line:
wh / carry_wh * 100. The watt-hours above against the 100 Wh an airline takes without approval. - The same capacity counted at 3.6 V:
ah * cell_v. If the label's 3.7 V is the higher figure Battery University describes, this is the watt-hours at the standard 3.6 V a cell. A label printed at 3.6 V gives the same number twice. - Largest capacity within 100 Wh at this voltage:
Math.floor(carry_wh / volts * mah_per_ah). 100 Wh divided by the voltage, back into mAh, rounded down so the figure stays inside the line. - Largest capacity within 160 Wh at this voltage:
Math.floor(approval_wh / volts * mah_per_ah). 160 Wh divided by the voltage, back into mAh, rounded down the same way.
What this cannot tell you
Every calculator has an edge, and a page that hides its edge is worse than no page at all. Here is this one's.
- It is arithmetic on the figures printed on the label. No battery was charged or drained for it, and this site has not handled these batteries itself.
- The answer is the energy stored in the cells. A power bank gives a phone noticeably less, because raising the cells' voltage to USB's and charging the phone both lose some; how much depends on the power bank and the phone, and this page does not guess it.
- It is only as right as the voltage you give it. Use the voltage printed beside the mAh, never the 5 V output, and when the label prints a Wh figure as well, that printed figure is the one an airline goes by.
- The 100 Wh and 160 Wh lines are the FAA's and IATA's for lithium-ion (rechargeable) batteries. Lithium metal batteries, the non-rechargeable kind, are limited by their lithium content instead, and this page does not cover them.
- Airlines may set stricter rules than these, such as fewer power banks per person or no charging from one on board, so check the airline's own page before you fly. Spare batteries and power banks go in carry-on, never in checked bags.
What that battery means for a flight
These follow from the answer above and nothing else. Each heading below covers one span of results, so read the one the calculator pointed you at and ignore the rest.
100 Wh or less: no airline approval needed
Inside the line the FAA and IATA set for a lithium-ion battery a passenger carries without asking. As a spare or a power bank it goes in your carry-on bag, never in checked luggage, and some airlines limit how many you bring or whether you can use one on board. The power banks below are ones this site has written about.
Anker PowerCore 10000 Review 2026, Still Worth It? covers this range in full.
Anker Zolo 20,000mAh vs Premium Power Banks 2026 covers this range in full.
UGREEN Nexode 25000 vs Anker Prime 27650, Which Is Worth It covers this range in full.
Over 100 Wh, up to 160 Wh: ask the airline first
Allowed only with the airline's approval, and the FAA limits spares this size to two per person. Larger laptop batteries and small portable power stations land here. Ask the airline before the day you fly. This site has not covered a battery this size, so it is not going to name one.
Over 160 Wh: not in passenger bags
The FAA and IATA rules do not allow a lithium-ion battery this size in a passenger's carry-on or checked bags. Portable power stations are often this big. If it has to travel by air, ask the airline or a shipping company how it can go; this site has not covered one, so it is not going to name one.
If the label already prints a Wh figure, that is the number an airline goes by, and it is a good check on the voltage you used here. A mAh to Wh converter can only be as right as that voltage, so take it from the label rather than the USB port. For the watt-hours in a UPS battery and how long they last under a load, the UPS calculator does that sum.
Questions about the mAh to Wh converter
How do I convert mAh to Wh?
Divide the mAh by 1,000 to get amp-hours, then multiply by the battery's voltage. A 10000 mAh power bank at 3.7 V is 10 Ah, and 10 x 3.7 is 37 Wh. A 20000 mAh one at the same voltage is 74 Wh. This is the formula the FAA and IATA publish, and the mAh to Wh converter above does it for any label.
Which voltage do I use to convert mAh to Wh?
The one printed on the battery beside the mAh, which for a lithium-ion power bank is its cell voltage, usually 3.6 or 3.7 V. Battery University gives 3.6 V as the standard figure for a lithium-ion cell and says 3.7 V raises the watt-hours on paper: 10000 mAh is 37 Wh at 3.7 V and 36 Wh at 3.6 V. Never use the 5 V USB output: that would give 50 Wh, more than the cells hold.
How many mAh can I take on a plane?
It depends on the voltage, because the airline rule is in watt-hours. The FAA and IATA allow a lithium-ion battery up to 100 Wh without approval, which at 3.7 V is 27,027 mAh and at 3.6 V is 27,777 mAh. Up to 160 Wh, or 43,243 mAh at 3.7 V, needs the airline's approval, with at most two such spares per person. Power banks go in carry-on, never in checked bags.
Is a 27650 mAh power bank under 100 Wh?
At 3.6 V it is 99.5 Wh, just inside the 100 Wh line an airline takes without approval. The same capacity counted at 3.7 V would be 102.3 Wh, over the line, so the voltage on the label decides it. If the label prints a Wh figure, that is the one the airline reads.
Why does a power bank charge a phone fewer times than mAh to Wh suggests?
Because the watt-hours are what the cells hold, not what reaches the phone. A 10000 mAh power bank holds 37 Wh at 3.7 V, but raising that to USB's voltage and charging the phone's own battery both lose some on the way, and how much depends on the power bank and the phone. Compare watt-hours to watt-hours, and expect fewer charges than the simple division gives.
Sources
- FAA PackSafe: lithium batteries: Sets the passenger limits: lithium-ion batteries up to 100 Wh are allowed, 101 to 160 Wh need the airline's approval with a limit of two spares per person, larger ones are forbidden, and spare batteries and power banks must be carried on, not checked.
- FAA PackSafe: batteries carried by airline passengers: Gives the formula, watt-hours = volts x amp-hours, says to divide a mAh figure by 1000 first, and works one example: 12 V at 8 Ah is 96 Wh.
- IATA Lithium Battery Guidance Document: Defines the watt-hour rating as the rated capacity in Ah times the nominal voltage, divides a mAh figure by 1000 (4400 mAh is 4.4 Ah), and requires the Wh rating to be marked on a lithium-ion battery's case.
- IATA Dangerous Goods Regulations, Table 2.3.A: The international table airlines apply to passengers' batteries, with the same 100 Wh and 160 Wh lines.
- Battery University BU-303: confusion with voltages: Explains that a standard lithium-ion cell is 3.60 V nominal and that the 3.70 V some labels print raises the watt-hours on paper without changing the battery.
- NIST: metric (SI) prefixes: Lists milli as one thousandth, which is why 1000 mAh is 1 Ah.
UPS Calculator 2026: How Long Your Battery Actually Lasts Anker Zolo 20,000mAh vs Premium Power Banks 2026
The picks above are collected in my Amazon storefront, so you are not hunting model numbers across five tabs.
