How to Use the Power Bank Charge Count Calculator
A 10,000mAh power bank won't charge a 3,500mAh phone exactly 2.85 times. That's because the power bank's internal cell voltage (typically 3.7V) differs from its USB output voltage (5V), and converting between them loses energy. In practice, only about 80-90% of the rated capacity is usable.
This calculator takes your power bank's capacity, your device's battery capacity, and a conversion efficiency (85% by default) to calculate the usable capacity and how many full charges you can expect. A result like 2.3x means 2 complete charges, with the remaining capacity good for roughly 30% of a third.
Fast-charging cables and adapters can push efficiency slightly higher, while budget power banks or cold environments can lower it. For the most accurate estimate, check the manufacturer's tested efficiency if it's listed on the product spec sheet.
Frequently Asked Questions
Converting power from the power bank's internal cell voltage to USB output voltage causes energy loss, so only about 80-90% of the rated capacity is actually usable. This calculator applies an 85% efficiency by default.
It means you get 2 full charges, and the remaining capacity is enough for roughly 30% of a third charge.