Wh to Ah Converter
Ah = Wh / V. 100 Wh at 3.7 V is 27.03 Ah (27,027 mAh), and a 20,000 mAh power bank at 3.7 V holds 74 Wh. IATA allows lithium-ion batteries up to 100 Wh in carry-on without approval and up to 160 Wh with airline approval.
How to use
- Choose the direction: Wh to Ah, or Ah (or mAh) to Wh.
- Enter the value and the battery voltage. For power banks and phone batteries use the cell voltage on the label, usually 3.6 V, 3.7 V or 3.85 V.
- Read the result and the carry-on check, which follows the IATA 100 Wh and 160 Wh limits for lithium-ion batteries.
How it works
Wh = Ah × V, and Ah = Wh / V. Example: 100 Wh at 3.7 V = 27.03 Ah (27,027 mAh).
mAh = Ah × 1000. A 20,000 mAh power bank at 3.7 V holds 20 × 3.7 = 74 Wh.
The voltage must be the one the Ah rating refers to. Power bank mAh figures are stated at the internal cell voltage (about 3.7 V), not at the 5 V USB output, so using 5 V would overstate the energy.
Flight check (IATA Lithium Battery Guidance Document): up to 100 Wh is allowed without approval; over 100 Wh up to 160 Wh needs airline approval and is limited to two spare batteries per person; over 160 Wh is not allowed on passenger aircraft. Spare batteries and power banks go in carry-on baggage only.
Power bank sizes and the flight limit
Watt-hours at a cell voltage of 3.7 V. If the label lists Wh, that printed value decides. Airlines can be stricter than IATA, so check their rules too.
| Rated capacity | Energy | Carry-on |
|---|---|---|
| 10,000 mAh | 37 Wh | Allowed |
| 20,000 mAh | 74 Wh | Allowed |
| 26,800 mAh | 99.2 Wh | Allowed |
| 27,000 mAh | 99.9 Wh | Allowed |
| 30,000 mAh | 111 Wh | Airline approval |
| 40,000 mAh | 148 Wh | Airline approval |
| 50,000 mAh | 185 Wh | Not allowed |
Source of the limits
The 100 Wh and 160 Wh thresholds come from the IATA Dangerous Goods Regulations, Table 2.3.A, summarised in the IATA Lithium Battery Guidance Document and the passenger guidance of aviation authorities such as the FAA. They apply to lithium-ion batteries. Lithium metal batteries use a lithium content limit instead (2 g, or 8 g with approval).
FAQ
How many mAh is 100 Wh?
At 3.7 V, 100 Wh is about 27,027 mAh, so most power banks up to 27,000 mAh are under the limit. At 3.6 V it is 27,778 mAh and at 3.85 V 25,974 mAh.
Can I take a 20,000 mAh power bank on a plane?
Yes. At 3.7 V it is 74 Wh, under 100 Wh, so it can go in your carry-on without airline approval. It must not go in checked baggage.
Is a 30,000 mAh power bank allowed?
At 3.7 V it is 111 Wh, which falls in the 100 to 160 Wh band. Many airlines allow it with prior approval, at most two spares per person. Check with your airline before flying.
Why does the voltage matter?
Amp-hours only describe charge. Energy is charge times voltage, so the same 10 Ah is 37 Wh at 3.7 V but 120 Wh at 12 V.
Which voltage should I use for a 12 V battery?
The nominal voltage on the label: 12 V for lead-acid, 12.8 V for a four-cell LiFePO4 pack. A 100 Ah LiFePO4 battery is 1,280 Wh.