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Power Bank Calculator
Estimate how many full charges a power bank will give your device. Real-world results are lower than the raw mAh figures because of conversion losses.
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Short answer: A 20,000 mAh power bank realistically recharges a typical smartphone 3 to 5 times — not the 6+ the raw numbers suggest. That’s because of conversion losses. Use the calculator below to get a number for your exact phone.
Why you don’t get the full capacity
Power banks store energy at 3.7 V but charge your phone at 5 V or higher. Converting voltage loses energy as heat, so real-world output is typically 60–85% of the label. Fast charging, a warm battery, and cable quality all reduce it further.
The math
Charges = (power bank mAh × efficiency) ÷ phone battery mAh.
For a 20,000 mAh bank at 80% efficiency charging a 3,200 mAh phone: (20,000 × 0.8) ÷ 3,200 = 5 full charges. A phone with a bigger 5,000 mAh battery would get about 3.2 charges from the same bank.
Real-world examples
| Phone battery | Approx. full charges from 20,000 mAh |
|---|---|
| 3,000 mAh (compact phone) | ~5.3 |
| 4,000 mAh (mid-size) | ~4.0 |
| 5,000 mAh (large/flagship) | ~3.2 |
Flying with it? A 20,000 mAh bank is about 74 Wh, so it’s fine in carry-on — see can you take a power bank on a plane.
Ready to buy? Compare Power Banks on Amazon.