mAh to Wh Calculator
Convert milliamp-hours (mAh) to watt-hours (Wh): Wh = mAh × V ÷ 1,000. Check power bank capacity for airline limits and compare phone and laptop batteries.
ENERGY
18.5 Wh
IN kWh
0.0185 kWh
FORMULA
Wh = mAh × V / 1000
mAh to Wh — Battery Table (3.7V Li-ion)
| mAh | Wh (3.7V) | Wh (3.85V) | Wh (7.4V) |
|---|---|---|---|
| 1,000 | 3.7 | 3.9 | 7.4 |
| 2,000 | 7.4 | 7.7 | 14.8 |
| 3,000 | 11.1 | 11.6 | 22.2 |
| 4,000 | 14.8 | 15.4 | 29.6 |
| 5,000 | 18.5 | 19.3 | 37 |
| 6,000 | 22.2 | 23.1 | 44.4 |
| 8,000 | 29.6 | 30.8 | 59.2 |
| 10,000 | 37 | 38.5 | 74 |
| 15,000 | 55.5 | 57.8 | 111 |
| 20,000 | 74 | 77 | 148 |
💡 How to Convert mAh to Wh
To convert mAh to Wh, multiply the milliamp-hours by the voltage and divide by 1,000. For phone batteries and power banks, use the lithium-ion cell's nominal voltage, usually 3.6–3.7 V, which is the voltage the mAh rating refers to.
mAh to Wh formula
Example: 20,000 mAh at 3.7 V → 20,000 × 3.7 ÷ 1,000 = 74 Wh
Worked examples
- 10,000 mAh power bank: 10,000 × 3.7 ÷ 1,000 = 37 Wh.
- Phone with a 5,000 mAh battery at about 3.85 V: 5,000 × 3.85 ÷ 1,000 = 19.25 Wh.
- 26,800 mAh power bank: 26,800 × 3.7 ÷ 1,000 = 99.16 Wh, just under the 100 Wh airline limit, which is why that size is so common.
mAh to Wh table, with airline carry-on status
| mAh | Wh @ 3.6 V | Wh @ 3.7 V | Wh @ 3.85 V | Carry-on (at 3.7 V) |
|---|---|---|---|---|
| 1,000 | 3.6 | 3.7 | 3.85 | Yes |
| 3,000 | 10.8 | 11.1 | 11.55 | Yes |
| 4,000 | 14.4 | 14.8 | 15.4 | Yes |
| 5,000 | 18 | 18.5 | 19.25 | Yes |
| 10,000 | 36 | 37 | 38.5 | Yes |
| 20,000 | 72 | 74 | 77 | Yes |
| 26,800 | 96.48 | 99.16 | 103.18 | Yes |
| 27,000 | 97.2 | 99.9 | 103.95 | Yes |
| 30,000 | 108 | 111 | 115.5 | Airline approval |
| 40,000 | 144 | 148 | 154 | Airline approval |
Flying with power banks
Under the rules used by the FAA and most airlines (based on IATA guidance), spare lithium-ion batteries and power banks must go in carry-on baggage, not checked bags. Batteries up to 100 Wh are allowed; 100–160 Wh need airline approval (usually limited to two spares); above 160 Wh they are not permitted for passengers. Airlines can set stricter rules, so check before you fly. Many power banks print the Wh value on the label for exactly this reason.
Why a power bank delivers less than its rated capacity
A power bank's mAh rating refers to its 3.7 V cells, but USB outputs 5 V or more, and voltage conversion and heat lose energy. In practice a phone typically receives roughly two-thirds to four-fifths of the power bank's rated Wh.