Power Bank Charging Calculator
Work out how many times a power bank will charge your phone - and roughly how long a full charge takes. Pick a capacity and your device to see realistic, real-world numbers.
Power bank charging chart
A power bank never delivers its full rated capacity to your phone. Energy is lost converting from the pack’s 3.7V cells up to 5V (or higher) charging voltage, plus cable and heat losses - so a real-world figure of around 65% of the rated mAh is realistic. The chart below assumes a typical 4,000 mAh smartphone.
| Power bank capacity | Usable (~65%) | Charges of a 4,000 mAh phone | Best for |
|---|---|---|---|
| 5,000 mAh | ~3,250 mAh | ~0.8 charges | Pocket top-up |
| 10,000 mAh | ~6,500 mAh | ~1.6 charges | A full day out |
| 20,000 mAh | ~13,000 mAh | ~3.2 charges | Weekend / multi-device |
| 26,800 mAh | ~17,400 mAh | ~4.3 charges | Travel (airline cabin limit) |
Branded power banks, made to your brand
Keep your logo in your customers’ hands all day. USB Makers supplies fully branded power banks in a range of capacities and finishes, with low minimum order quantities, fast turnaround and worldwide delivery. Request a quote and we will recommend the right capacity for your campaign.
Request a quoteFrequently asked questions
How many times can a 10,000 mAh power bank charge my phone?
For a typical 4,000 mAh smartphone, expect around 1.5–1.7 full charges from a 10,000 mAh power bank, once real-world conversion losses are taken into account. Larger phones get slightly fewer charges; smaller phones get a little more.
Why does not a 10,000 mAh power bank give my phone 10,000 mAh?
The cells inside a power bank store energy at about 3.7V, but your phone charges at 5V or higher. Converting between voltages loses energy as heat, and the cable adds a little more. After these losses you can realistically use around 65% of the rated capacity, which is why our calculator builds that in.
How long does a power bank take to charge a phone?
It depends on the charging output and your phone’s battery size. A 4,000 mAh phone at a standard 10W (2A) output takes roughly 2.5 hours for a full charge; a faster 18W output is quicker. Use the calculator above for your exact combination.
What size power bank do I need?
For a single daily top-up, 5,000–10,000 mAh is plenty. For multiple charges, several devices or a long trip, choose 20,000 mAh or more - but note that airlines cap cabin power banks at around 27,000 mAh (100Wh).
Can I get power banks branded with my logo?
Yes. We supply fully branded power banks and other branded tech with your logo, in a choice of capacities and finishes. Low minimum order quantities, fast turnaround and worldwide delivery.
