Convert power-bank mAh to Wh before you fly
Read the manufacturer’s printed watt-hour (Wh) rating first. If none is given, calculate Wh by multiplying the capacity in milliampere-hours (mAh) by its matching nominal voltage, then dividing by 1,000. Check the result against your operating airline’s rules: a calculation helps identify capacity, but does not give permission to fly.
Guidance checked 13 November 2026. This guide explains the calculation using published guidance and hypothetical examples; it does not assess or test individual power banks.
Illustration: AI-generated conceptual artwork; not a product photograph or evidence of hands-on testing.
Read the units before doing the maths
mAh measures electrical charge; ampere-hours (Ah) express the same quantity on a larger scale, with 1Ah equal to 1,000mAh. Wh measures stored energy. Watts (W) describe power, including charging rate. A prominent W charging-speed claim therefore tells you something different from the Wh capacity needed for an energy limit.
The formula is Wh = mAh × matching nominal V ÷ 1,000. If the label gives Ah instead, use Wh = Ah × V. Both forms appear in the UK Civil Aviation Authority’s packing guidance.
The crucial step is finding the voltage that belongs to the stated capacity. Look on the case, in the manual or in the manufacturer’s technical specifications. Do not substitute a USB output voltage such as 5V or 9V, and do not combine a cell’s capacity with a voltage specified for a different pack configuration. The two figures must describe the same battery arrangement.
Four assumed examples
Every row below is a hypothetical calculation with an explicitly assumed matching nominal voltage. These are not real product specifications or measured ratings. Use the method with your own manufacturer’s figures, rather than choosing whichever example resembles the capacity on your power bank.
| Example | Assumed capacity | Assumed matching nominal voltage | Calculated energy |
|---|---|---|---|
| Assumed example 1 | 20,000mAh | 3.7V | 74Wh |
| Assumed example 2 | 20,000mAh | 3.85V | 77Wh |
| Assumed example 3 | 26,800mAh | 3.7V | 99.16Wh |
| Assumed example 4 | 26,800mAh | 3.85V | 103.18Wh |
The two 26,800mAh examples show why the mAh figure alone cannot settle the decision. At 3.7V, the result is 99.16Wh; at 3.85V, it is 103.18Wh. The higher matching voltage puts the second example above 100Wh. Keep those exact results when comparing them with a limit: do not round across the boundary, assume every power bank uses 3.7V or assume every 26,800mAh unit falls below 100Wh.
Apply the result to your journey
As a Singapore-scoped example, the Civil Aviation Authority of Singapore’s packing guidance allows power banks of not more than 100Wh subject to its other conditions, requires airline approval above 100Wh through 160Wh, and prohibits those above 160Wh. These bands are not worldwide clearance; capacity is only one carriage condition.
The US FAA’s lithium-battery guidance notes that newer lithium-ion batteries carry printed Wh ratings and explicitly warns that airlines can impose stricter quantity or Wh limits. Check every operating carrier on your itinerary, together with relevant departure and transit requirements.
Short pre-flight checklist
- Find the manufacturer-printed Wh rating first.
- If needed, identify matching mAh and nominal-voltage figures and calculate without rounding across a limit.
- If ratings are missing, unclear or inconsistent, seek manufacturer and airline confirmation; do not guess the voltage.
- Confirm the conditions for all operating flights before packing.
Conversion does not establish safety certification, replace a manufacturer’s label or secure airline approval. Nor does nominal stored energy guarantee the energy delivered to your phone or laptop: conversion and other losses prevent a simple promise of recharge counts or runtime. Anker’s technical explanation of mAh and Wh explains these distinctions; it is a formula reference, not a product recommendation.
