Power Bank Charges Calculator
How many times a power bank can really charge your phone, its energy in watt-hours and whether you can take it on a plane.
Results
Full phone charges
3.63
Energy stored
74.0
Wh
Real capacity at the 5 V output
12,580
mAh
Air travel (cabin baggage)
Up to 100 Wh — normally allowed in the cabin
What this tool does
The mAh printed on a power bank is measured at its cells' 3.6–3.7 V, not at the 5 V (or higher) it delivers through USB, and the voltage conversion loses roughly 10 to 20 % as heat. That is why a '20 000 mAh' bank gives about three and a half charges to a 4500 mAh phone, not four and a half. Airlines limit power banks by watt-hours: under the IATA rules up to 100 Wh is normally fine in cabin baggage, 100–160 Wh needs approval, and power banks never go in checked luggage.
Formula
Wh = mAh × V ÷ 1000 · charges = Wh_bank × efficiency ÷ Wh_phone
Variables
| Symbol | Meaning | Unit |
|---|---|---|
bc | Power bank capacity | mAh |
bv | Voltage per cell | V |
ef | Efficiency | % |
pc | Phone battery capacity | mAh |
pv | Phone battery voltage | V |
CH | Full phone charges | — |
WH | Energy stored | Wh |
C5 | Real capacity at the 5 V output | mAh |
FL | Air travel (cabin baggage) | — |
Worked example
- Power bank capacity20,000 mAh
- Voltage per cell3.7 V
- Efficiency85 %
- Phone battery capacity4500 mAh
- Phone battery voltage3.85 V
- Full phone charges3.63
- Energy stored74.0 Wh
- Real capacity at the 5 V output12,580 mAh
- Air travel (cabin baggage)Up to 100 Wh — normally allowed in the cabin
Limitations
- Coverage and consumption figures vary between products. Take the values from the manufacturer's datasheet for the product you are actually using.
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.