Enter a battery's milliamp-hour rating and its nominal voltage to find its energy content in watt-hours.
How to Use the Milliamp-Hours to Watt-Hours Calculator
Enter the milliamp-hour rating from the label and set the voltage — 3.7 V loads by default, the typical nominal voltage for a single lithium-ion cell, but change it if the pack is built differently. The watt-hour figure updates immediately.
The Number on Airline Battery Rules
Power banks and phone batteries are marketed almost entirely in mAh, but the actual energy-content limits that matter — airline carry-on rules chief among them — are written in watt-hours, because mAh alone says nothing about energy without a voltage attached. A power bank rated 20,000 mAh at a 3.7 V nominal cell voltage works out to 74 Wh, comfortably inside the commonly cited 100 Wh carry-on threshold; a bank built around a higher cell voltage would report a different Wh figure from the identical mAh number.
Energy (Wh) = (Milliamp-Hours ÷ 1,000) × Voltage3.7 V is a nominal figure, not a universal one — some lithium chemistries and multi-cell packs run at other voltages, and the manufacturer's own spec sheet is the authority when the two disagree. Treat the default here as a reasonable starting point for a single-cell lithium pack, not a fixed constant.