Wh to mAh Calculator
Convert watt-hours to mAh and check any power bank against the 100 Wh airline limit and the 2026 ICAO rules.
Quick answer
To convert watt-hours to mAh, multiply the Wh by 1,000 and divide by the voltage. mAh = Wh × 1,000 ÷ V. The 100 Wh airline limit equals 27,027 mAh at 3.7 V, 27,778 mAh at 3.6 V and 25,974 mAh at 3.85 V. That is why the biggest travel power banks are sold at about 25,600 to 27,000 mAh.
How to use the Wh to mAh calculator
- Enter the energy in Wh. Type the watt-hour rating printed on the battery or power bank, often in small print on the back, such as 74 Wh or 99.9 Wh. To check the airline limit itself, leave it at 100 Wh.
- Enter the nominal voltage. Use the cell voltage, normally 3.6 V, 3.7 V or 3.85 V for a power bank or phone. Laptop packs use 11.1 V to 15.4 V. Do not use the 5 V, 9 V or 20 V USB output voltage.
- Read the capacity in mAh. The large number is the milliamp-hour rating. The chip shows how that Wh compares with airline rules, and the cards give the Ah, the largest mAh that fits under 100 Wh at your voltage and the share of the limit used.
Wh to mAh formula
Watt-hours measure energy. Milliamp-hours measure charge. Dividing energy by voltage gives charge in amp-hours, and multiplying by 1,000 turns amp-hours into milliamp-hours.
Where:
- mAh is the charge capacity in milliamp-hours.
- Wh is the rated energy in watt-hours.
- V is the nominal cell or pack voltage.
- Ah is the charge capacity in amp-hours.
The opposite direction, finding Wh from a mAh rating, is the mAh to Wh calculator.
Worked examples
Example 1: the 100 Wh airline limit
You want the largest power bank you can fly with, built from 3.7 V cells.
Anything up to about 27,000 mAh at 3.7 V stays at or under 100 Wh. A bank rated 27,000 mAh is 99.9 Wh. With 3.85 V cells the ceiling drops to 25,974 mAh, which is why some brands stop at 25,600 mAh (98.56 Wh at 3.85 V).
Example 2: a 99 Wh power bank
A label reads 99 Wh with 3.6 V cells.
The same 99 Wh at 3.7 V would be printed as 26,757 mAh. The energy is identical, so both banks charge your devices the same amount despite the different mAh ratings.
Example 3: 65 Wh laptop battery
A laptop has a 65 Wh battery. In 3.7 V power bank terms:
So a 20,000 mAh bank (74 Wh) holds a little more energy than the laptop battery. After losses of 15% to 25% over USB-C, expect one full laptop charge or a bit less. At the laptop’s own 11.4 V the battery is 5,702 mAh.
Wh to mAh conversion table
Values in mAh, calculated as Wh × 1,000 ÷ V and rounded to the nearest whole number. The 100 Wh and 160 Wh rows mark the airline thresholds.
| Energy (Wh) | 3.6 V | 3.7 V | 3.85 V | 7.4 V | 11.1 V |
|---|---|---|---|---|---|
| 10 | 2,778 | 2,703 | 2,597 | 1,351 | 901 |
| 20 | 5,556 | 5,405 | 5,195 | 2,703 | 1,802 |
| 37 | 10,278 | 10,000 | 9,610 | 5,000 | 3,333 |
| 50 | 13,889 | 13,514 | 12,987 | 6,757 | 4,505 |
| 74 | 20,556 | 20,000 | 19,221 | 10,000 | 6,667 |
| 99 | 27,500 | 26,757 | 25,714 | 13,378 | 8,919 |
| 100 | 27,778 | 27,027 | 25,974 | 13,514 | 9,009 |
| 160 | 44,444 | 43,243 | 41,558 | 21,622 | 14,414 |
Airline rules for power banks (as of October 2026)
Airlines regulate batteries by watt-hours, not mAh, which is the main reason people need this conversion.
The 100 Wh line
The FAA PackSafe guidance limits lithium-ion batteries and power banks to 100 Wh each in carry-on bags, with up to two spares of 101 to 160 Wh allowed only with airline approval. Spare batteries and power banks are banned from checked bags, and if your carry-on is gate checked they must come out and stay with you.
New ICAO limits from March 2026
An ICAO addendum in force since 27 March 2026 tightened the rules internationally. The IATA guidance to operators sets a maximum of two power banks per passenger, says they must not be recharged on board and should not be used to charge other devices in flight, and requires each one to be protected against short circuits. IATA also states that the option to carry 101 to 160 Wh power banks with operator approval will be dropped from 1 January 2027, leaving 100 Wh as the hard ceiling.
Airlines can be stricter
Some carriers have announced tighter limits of their own, such as one power bank per passenger or a ban on using them in the cabin. Check your airline’s page before you fly, especially for anything between 90 and 100 Wh where label rounding could cause an argument at the gate.
What affects the result
The voltage on the label
Power banks list both the cell voltage and a 5 V USB rating. Use the cell voltage. Dividing 100 Wh by 5 V gives 20,000 mAh, which understates the true cell capacity by about 26% and makes a bank look smaller than it is.
Rated versus delivered energy
The Wh on the case is the energy stored in the cells. Expect 60% to 80% of it to reach your phone or laptop after boost conversion and charging losses. To estimate how long that energy runs a device, use the battery life calculator.
Frequently asked questions
How many mAh is 100 Wh?
100 Wh is 27,027 mAh at 3.7 V, 27,778 mAh at 3.6 V and 25,974 mAh at 3.85 V. For a laptop battery at 11.1 V it is 9,009 mAh. The voltage on your battery label decides which figure applies, so enter it in the calculator rather than assuming 3.7 V.
Can I take a 30,000 mAh power bank on a plane?
At 3.7 V, 30,000 mAh is 111 Wh, over the 100 Wh limit. Some airlines may approve it until the end of 2026, but IATA guidance removes the approval route for 101 to 160 Wh power banks from 1 January 2027. In practice, choose a bank of 27,000 mAh or less.
Where do I find the Wh rating on a power bank?
It is usually printed on the back or side among the regulatory text, as “Rated energy” or simply a figure in Wh. If only mAh and voltage are shown, multiply them and divide by 1,000. Airport security staff look for the Wh figure, so a bank without one may be refused.
How many mAh is a 160 Wh battery?
At 3.7 V, 160 Wh is 43,243 mAh. At 14.4 V, a common camera and drone pack voltage, it is 11,111 mAh. Batteries over 160 Wh cannot travel in passenger baggage at all. The mAh to kWh calculator helps for larger packs such as e-bike batteries.
Why does my 100 Wh bank show a different mAh than another 100 Wh bank?
They use cells with different nominal voltages. A bank with 3.6 V cells prints about 27,778 mAh for 100 Wh, while one with 3.85 V cells prints 25,974 mAh. Both store the same energy and will charge your devices the same amount. Compare power banks by Wh, not mAh.