kWh to mAh Converter (Battery Wh and mAh)
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Flying with it, and how long it lasts
A conversion and sizing aid, not an electrical design. Wiring, breaker and cable choices depend on the cable type, length, installation method and local rules: have a licensed electrician check any new circuit.
mAh = Wh ÷ volts × 1,000, and 1 kWh = 1,000 Wh. At a lithium-ion cell’s 3.7 V, 100 Wh is 27,027 mAh and a 20,000 mAh power bank holds 74 Wh. The same 100 Wh is 8,333 mAh at 12 V: without the voltage, mAh and kWh cannot be converted.
Phones and power banks are sold in milliamp-hours, laptops and e-bikes in watt-hours, home and van batteries in amp-hours or kilowatt-hours. They only line up once you bring in the battery’s voltage. The converter does that, then checks the result against the US flight limits and tells you roughly how long the battery will run a device.
How to convert kWh or Wh to mAh
| To find | Formula | Example |
|---|---|---|
| mAh from Wh | mAh = Wh ÷ V × 1,000 | 100 Wh ÷ 3.7 V × 1,000 = 27,027 mAh |
| mAh from kWh | mAh = kWh × 1,000,000 ÷ V | 1.2 kWh ÷ 12 V × 1,000,000 = 100,000 mAh |
| Wh from mAh | Wh = mAh × V ÷ 1,000 | 20,000 mAh × 3.7 V ÷ 1,000 = 74 Wh |
| Wh from Ah | Wh = Ah × V | 100 Ah × 12.8 V = 1,280 Wh |
Amp-hours and milliamp-hours measure charge; watt-hours and kilowatt-hours measure energy. Energy = charge × voltage, so the voltage is the bridge. Use the battery’s nominal voltage, the one printed on it: most phone and power-bank cells are 3.6 to 3.85 V, 12 V lead-acid batteries 12 V, and 12 V lithium iron phosphate (LiFePO4) packs 12.8 V.
Power banks: mAh to Wh and the flight limit
Power bank capacities are quoted in mAh at the cell voltage, usually 3.6 or 3.7 V. Airlines work in watt-hours. The FAA allows lithium-ion batteries of up to 100 Wh each in carry-on, in a device or as spares; between 101 and 160 Wh you need the airline’s approval and may carry up to two spares; above 160 Wh they are forbidden in passenger baggage. Spare batteries and power banks must go in carry-on, never in checked bags.
| Capacity | Wh at 3.7 V | Wh at 3.85 V | Within 100 Wh at 3.7 V? |
|---|---|---|---|
| 3,000 mAh | 11.1 | 11.6 | ✓ |
| 5,000 mAh | 18.5 | 19.2 | ✓ |
| 10,000 mAh | 37 | 38.5 | ✓ |
| 20,000 mAh | 74 | 77 | ✓ |
| 25,000 mAh | 92.5 | 96.2 | ✓ |
| 26,800 mAh | 99.2 | 103.2 | ✓ |
| 30,000 mAh | 111 | 115.5 | approval |
| 40,000 mAh | 148 | 154 | approval |
| 50,000 mAh | 185 | 192.5 | ✗ |
So at 3.7 V a power bank much above 27,000 mAh crosses 100 Wh. If the bank prints its Wh rating, use that figure: it is what security staff check.
Why a 20,000 mAh power bank does not give 20,000 mAh to your phone
The 20,000 mAh is measured at the cells’ 3.7 V, which is 74 Wh. USB delivers it at 5 V or more, so even with no losses the same energy is only 14,800 mAh at 5 V, and the conversion inside the bank loses some as heat. Charging a phone also loses energy. So a 20,000 mAh bank charges a phone with a 5,000 mAh battery fewer times than 20,000 ÷ 5,000 = 4 would suggest. Where the maker gives a rated output capacity, use it.
Home, van and e-bike batteries
Larger batteries are rated in amp-hours (Ah) or kWh. A 100 Ah battery holds 1,200 Wh at 12 V or 1,280 Wh at 12.8 V (LiFePO4). Divide by the load in watts for a rough runtime: 1,200 Wh runs a steady 60 W load for about 20 hours before losses. Lead-acid batteries should not be run flat, so only part of their capacity is usable; lithium iron phosphate can use most of it.
| Energy | mAh, 3.7 V | mAh, 12 V | Ah, 12.8 V | Ah, 48 V |
|---|---|---|---|---|
| 10 Wh | 2,703 | 833 | 0.8 | 0.2 |
| 50 Wh | 13,514 | 4,167 | 3.9 | 1 |
| 74 Wh | 20,000 | 6,167 | 5.8 | 1.5 |
| 100 Wh | 27,027 | 8,333 | 7.8 | 2.1 |
| 160 Wh | 43,243 | 13,333 | 12.5 | 3.3 |
| 500 Wh | 135,135 | 41,667 | 39.1 | 10.4 |
| 1,000 Wh | 270,270 | 83,333 | 78.1 | 20.8 |
| 1,200 Wh | 324,324 | 100,000 | 93.8 | 25 |
| 5,000 Wh | 1,351,351 | 416,667 | 390.6 | 104.2 |
Running a mains appliance from a battery through an inverter draws watts ÷ battery volts from the battery, plus the inverter’s losses: a 600 W load takes 50 A from a 12 V battery before losses, which is why big inverters run on 24 or 48 V. For home batteries, see the home battery calculator; for portable units, our guide to portable power stations.
Common mistakes
- Comparing mAh across voltages. 10,000 mAh at 3.7 V is 37 Wh; 10,000 mAh at 12 V is 120 Wh.
- Using the USB 5 V to convert a power bank’s rated mAh. The rating is at the cell voltage.
- Forgetting the factor of 1,000 between mAh and Ah, and between Wh and kWh.
- Assuming all of a battery is usable. Conversion losses, and the depth of discharge a battery tolerates, cut the real figure.
Standards and data sources
| What | Source | Version |
|---|---|---|
| Batteries on flights | FAA PackSafe: lithium batteries | Page updated 11 August 2026 |
The conversions are exact physics and need no data. The running cost and CO₂ use figures stored in the GreenCalculus MasterBrain with their source cells, read live by the converter, so they update when the publishers do. The breaker check follows the code text; it is a sizing aid, not a design, and a licensed electrician should check any new circuit.
Frequently asked questions
At 3.7 V, 270,270 mAh (1,000 Wh ÷ 3.7 V × 1,000). At 12 V, 83,333 mAh. The answer depends on the battery voltage.
74 Wh at the usual 3.7 V cell voltage (20,000 × 3.7 ÷ 1,000). That is under the FAA’s 100 Wh carry-on limit.
At 3.7 V it holds 111 Wh, over the FAA’s 100 Wh limit, so in the US you need the airline’s approval (allowed between 101 and 160 Wh, carry-on only). Check the Wh printed on the bank.
Multiply by the voltage and divide by 1,000: Wh = mAh × V ÷ 1,000.
In the US, 100 Wh per battery without approval, which is about 27,000 mAh at 3.7 V. Up to two spares of 101 to 160 Wh with the airline’s approval. Spares go in carry-on only.
1,200 Wh (1.2 kWh) at 12 V, and 1,280 Wh at 12.8 V for a lithium iron phosphate battery.