Power Bank Recharges Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/10/2026
The number of recharges is calculated with (power bank capacity × conversion efficiency) ÷ phone capacity, rounded down to the nearest whole number. A 10,000 mAh power bank with 70% efficiency provides 2 full recharges of a 3,000 mAh phone.
Explanation
The nominal capacity printed on a power bank (in mAh) is never fully delivered to the phone it charges: some energy is lost during voltage conversion (the internal cells run at 3.7V, while the USB output delivers 5V, 9V, or 12V depending on the fast-charging protocol), plus additional losses in the cable and the power bank's protection circuitry. This conversion efficiency typically ranges from 60% for an entry-level model to 85% for a premium model with optimized circuits, with this calculator using 70% as a cautious default baseline, adjustable to your device's actual quality. This calculation complements our battery life calculator, which answers a different question (how long a device lasts under a given continuous power draw) rather than the number of discrete recharges a portable energy reserve can provide. In practice, a 10,000 mAh power bank (one of the most common capacities on the market) typically provides 2 full recharges of a modern smartphone, rather than the 3.3 recharges a simple division ignoring losses would suggest. The time needed to then recharge this same power bank once it's empty is calculated separately with our battery charging time calculator.
Example: a 10,000 mAh power bank, a 3,000 mAh phone
Inputs
Power bank capacity: 10,000 mAh. Phone capacity: 3,000 mAh. Conversion efficiency: 70%.
Calculation
Usable capacity = 10,000 × 70% = 7,000 mAh. Number of recharges = 7,000 ÷ 3,000 ≈ 2.33, rounded down to 2 full recharges.
Result
This power bank provides 2 full recharges of the phone, with the third staying partial.
Frequently asked questions
Why isn't the capacity printed on the box ever fully usable?
Because a power bank's internal cells run at 3.7V, while the USB output must deliver 5V or more: this voltage conversion, handled by an internal electronic circuit, systematically dissipates part of the energy as heat, on top of additional losses in the charging cable used.
Why is the result rounded down to the nearest whole number?
Because a partial recharge (say, 0.33 of an extra recharge) doesn't fully charge a second device: this calculator only counts full recharge cycles actually obtained, with the capacity left over after the last full cycle still being useful for a partial top-up in practice.
Does fast charging reduce the number of recharges obtained?
Fast charging (higher voltages like 9V or 12V) can slightly reduce conversion efficiency compared to standard 5V charging, since conversion losses are generally a bit higher at higher output voltages. This effect remains secondary compared to the power bank's overall conversion circuit quality, the factor that most influences overall efficiency.