mAh to kWh Converter

This mAh to kWh converter turns the milliamp-hour rating on a phone, power bank, drone or laptop battery into energy you can compare: watt-hours (Wh) and kilowatt-hours (kWh). It also runs the conversion in reverse, from kWh to mAh, and flags whether the battery is within the FAA carry-on limits for air travel.

How to convert mAh to Wh and kWh

A milliamp-hour (mAh) measures charge, not energy: 1 mAh is 3.6 coulombs (NIST SP 811). To get energy you need the battery voltage:

• Wh = mAh × V ÷ 1,000
• kWh = mAh × V ÷ 1,000,000
• mAh = kWh × 1,000,000 ÷ V
• Ah = mAh ÷ 1,000

Use the nominal cell voltage printed on the battery. Most lithium-ion cells are 3.6–3.85 V (Battery University), and power banks are rated at the cell voltage, not the 5 V USB output.

Worked example with the default values

1. Capacity: 20,000 mAh, voltage 3.7 V
2. Watt-hours: 20,000 × 3.7 ÷ 1,000 = 74 Wh
3. Kilowatt-hours: 74 ÷ 1,000 = 0.074 kWh
4. Amp-hours: 20,000 ÷ 1,000 = 20 Ah
5. Reverse: 0.1 kWh at 3.7 V = 100,000,000 ÷ 3.7 ÷ 1,000 ≈ 27,027 mAh
6. Air travel: 74 Wh is at or under 100 Wh, so it is within the carry-on limit

mAh to Wh and kWh conversion table (3.7 V)

Airline limits for lithium batteries

FAA PackSafe guidance limits lithium-ion batteries to 100 Wh each for most passengers. With airline approval, you may carry up to two spare batteries of 101–160 Wh. Larger lithium-ion batteries are generally forbidden in passenger baggage. Spare batteries and power banks belong in carry-on bags, not checked luggage (FAA packing poster). Airlines can set stricter rules, so check your carrier before you fly.

What affects real-world capacity

• Conversion losses. Stepping 3.7 V up to 5 V USB or higher for USB-C Power Delivery loses energy as heat, so the device receives less than the rated Wh.
• Age and temperature. Lithium cells lose capacity with cycles and deliver less when cold.
• Rated vs tested. Some cheap power banks overstate mAh. A USB power meter shows what actually comes out.

From small cells to big batteries

The same math scales up. Home and solar batteries are rated in amp-hours (Ah) at 12, 24 or 48 V, or directly in kWh. Use the amp hours to kWh converter for those, and the battery runtime calculator to see how long one will run a load. Our off-grid solar system guide shows how battery banks store clean, renewable energy for later, and what is a kilowatt-hour explains the unit itself.

Step-by-step: checking a power bank before a flight

1. Look for a Wh figure on the case. If it is there, use it.
2. If only mAh is listed, find the cell voltage (often 3.6, 3.7 or 3.85 V).
3. Multiply mAh by volts and divide by 1,000 to get Wh.
4. Compare with 100 Wh and 160 Wh, then pack the bank in your carry-on.

References

• Thompson, A. & Taylor, B. N. (2008). Guide for the Use of the International System of Units (SI). NIST Special Publication 811. doi:10.6028/NIST.SP.811e2008
• Federal Aviation Administration. PackSafe: Lithium batteries. faa.gov

mAh vs kWh: what’s the difference?

mAh measures electric charge; kWh measures energy. Converting between them needs the voltage, so mAh only compares batteries of the same voltage. Two batteries with the same mAh can hold very different amounts of energy. A 10,000 mAh power bank at 3.7 V holds 37 Wh, while a 10,000 mAh (10 Ah) pack at 12 V holds 120 Wh, more than three times as much. Watt-hours and kilowatt-hours include the voltage, so they are the fair way to compare batteries of any size, from earbuds to electric cars.