Power bank calculator
A rough estimate of how many phone charges you might get. Real results vary by cable, phone age, cold weather, and charging speed.
Estimate only. Power-bank labels are usually in milliamp-hours (mAh) at about 3.7 V (the internal cells). Phones charge over USB at about 5 V, and conversion is not perfect. This tool assumes roughly 65% of the labeled mAh is usable at the phone (a mid-point in a common ~60–70% range). That is a planning assumption, not a lab measurement.
Often printed in Settings → About, or on the maker’s site. Many modern phones are ~3000–5000 mAh.
Enter values and tap Calculate.
How the estimate is made
- Usable bank mAh ≈ labeled bank mAh × efficiency (default 0.65).
- Full charges (total) ≈ usable bank mAh ÷ phone battery mAh.
- Per phone ≈ total charges ÷ number of phones.
Cold weather and fast charging can lower real-world results. Keep a torch and radio that do not depend on your phone.