Use the nominal battery voltage that belongs to the capacity rating on your label. 3.7 V is a common example, not a universal default. A printed manufacturer Wh rating is preferable to guessing.
A small voltage difference changes the answer
20,000 mAh at 3.7 V equals 74 Wh. At 3.85 V, it equals 77 Wh. Both calculations are correct for their respective inputs; only the device label tells you which inputs describe your battery.
What if the label only lists output voltages?
A list such as 5 V, 9 V and 12 V commonly describes charging outputs. Do not choose the smallest number to obtain a preferred result. Find the manufacturer’s exact model specification or ask the airline what documentation it accepts.
Using the website shortcut
The “Use 3.7 V” button fills an example value for convenience. Select it only after checking your label. You can overwrite it with the actual nominal voltage at any time; the calculator updates the energy result.
Which power bank voltage should you use to calculate Wh?
Use the nominal battery voltage that belongs to the capacity rating on your label. 3.7 V is a common example, not a universal default. A printed manufacturer Wh rating is preferable to guessing.
A small voltage difference changes the answer
20,000 mAh at 3.7 V equals 74 Wh. At 3.85 V, it equals 77 Wh. Both calculations are correct for their respective inputs; only the device label tells you which inputs describe your battery.
What if the label only lists output voltages?
A list such as 5 V, 9 V and 12 V commonly describes charging outputs. Do not choose the smallest number to obtain a preferred result. Find the manufacturer’s exact model specification or ask the airline what documentation it accepts.
Using the website shortcut
The “Use 3.7 V” button fills an example value for convenience. Select it only after checking your label. You can overwrite it with the actual nominal voltage at any time; the calculator updates the energy result.
Where can I check the official rule?
Use the FAA PackSafe — watt-hour calculation source linked above and confirm with every operating airline on your itinerary.
Independent guidance, not airline approval. Confirm with your operating airline before travel. Report a correction.
