Every power bank you’ve ever seen is sold on mAh. Every airline rule that decides whether it boards with you is written in Wh. The gap between those two units is where travelers get burned: a “27,650mAh” bank sounds like a bigger number of the same thing as a “26,800mAh” bank, but one of them computes to just over the US carry-on limit and the other squeaks under it by less than one watt-hour. Here’s the rule, the math, and where popular banks actually land — with the full sortable numbers in our power bank spec table.
The rule: 100Wh, carry-on only
US hazmat regulations (49 CFR, enforced by the FAA and screened by the TSA) treat power banks as spare lithium-ion batteries, and the framework most airlines worldwide mirror has three tiers:
- Up to 100Wh: allowed in carry-on baggage without airline approval. This covers the overwhelming majority of consumer power banks.
- 101–160Wh: allowed in carry-on only with airline approval, and typically capped at two spare batteries per passenger. This band exists mainly for large camera batteries and the biggest laptop banks.
- Over 160Wh: not allowed as passenger baggage at all — cargo rules apply.
Two universals sit on top of the tiers. First, spare lithium batteries — which is what a power bank is — are never allowed in checked baggage, at any size. A lithium fire in the cabin can be caught and contained by crew; one in the hold cannot, which is the entire logic of the rule. Second, individual airlines can be stricter than the regulation (some carriers have added in-flight usage or stowage restrictions), so the 100Wh line is the floor of what you must satisfy, not always the whole story.
The math: mAh × 3.7V ÷ 1000
Watt-hours are energy: capacity (amp-hours) times voltage. Power bank cells are lithium-ion with a nominal voltage of 3.7V, so the conversion airlines, manufacturers, and the label on the bank itself all use is:
Wh = mAh × 3.7 ÷ 1000
A 10,000mAh bank is 37Wh. A 20,000mAh bank is 74Wh. A 27,000mAh bank is 99.9Wh — which tells you exactly why so many “travel” power banks cluster at 26,800mAh (99.2Wh) and why nothing mainstream ships at 28,000mAh. The 100Wh limit, run backwards through the formula, works out to about 27,027mAh. That’s the real ceiling for an approval-free carry-on bank.
Most reputable manufacturers print the Wh figure directly on the casing, and that printed number is what a gate agent will look for. If a bank states only mAh, the nominal-3.7V computation is the accepted basis — but a bank with no markings at all can be refused at the checkpoint regardless of its actual size.
Why claimed mAh isn’t what your phone receives
A separate confusion, worth untangling because it trips up the same buyers: the mAh on the box is the rating of the cells inside at 3.7V, not the energy that comes out of the USB port. Delivering power at 5V (or 9V, or 20V for laptops) requires boosting the cell voltage, and that conversion plus cable and heat losses typically eats 20–35% of the rated energy. A 20,000mAh bank will realistically deliver something like 13,000–15,000mAh worth of phone charging, not four full charges of a 5,000mAh phone.
For airline purposes, though, the rated figure is the right one — the regulation cares about the energy stored in the cells (the fire risk), not the energy that survives conversion. So the claimed mAh understates what you’ll wish for and exactly states what the FAA counts.
The edge cases in our data
Our spec table covers popular banks from
Anker, Ugreen, Baseus, INIU, Belkin, Mophie, Samsung, Zendure, and
Shargeek, with a Carry-on OK column derived from each bank’s rated Wh.
Nearly everything clears the limit comfortably — 20,000mAh/74Wh is the
high-capacity sweet spot — but two rows deserve a closer look:
- Anker Prime Power Bank (27K, 250W), A1340 — computes to ~102.3Wh. Anker doesn’t publish a Wh figure on the product page; 27,650mAh at nominal 3.7V works out to 102.3Wh, just over the line. That’s consistent with Anker’s own FAQ declining to guarantee airline carry-on eligibility for this unit in all markets. It falls into the 101–160Wh approval band: many airlines will allow it if you ask, but it is not automatically fine the way a 74Wh bank is. If you fly often, this is the bank to think twice about.
- Zendure SuperTank Pro (26,800mAh, 100W) — 99.2Wh. Under the limit, but by less than a single watt-hour. Our table marks it carry-on OK based on the computed figure; before relying on it for travel, check the Wh printed on the unit itself, since the label is what screening staff go by.
Everything else in the table with 20,000–25,600mAh of claimed capacity — including 100W+ laptop-class banks like the Baseus Blade (74Wh) and the Shargeek Storm 2 (a maker-published 93.5Wh, explicitly marketed as TSA/FAA compliant) — sits safely under 100Wh. The carry-on-safe high-capacity view of the table filters to exactly that sweet spot: 20,000mAh or more, 100Wh or less.
The practical checklist
- Carry-on, never checked. No exceptions, any size.
- Find the Wh on the casing. If it’s ≤100Wh, you’re clear on any major airline without asking.
- Only mAh printed? Multiply by 3.7, divide by 1000. Under 27,000mAh is under 100Wh.
- 101–160Wh? Contact the airline before you fly; approval is commonly granted but is theirs to give, and two spares is the cap.
- Unmarked bank? Leave it home. Screening staff can’t verify what they can’t read.