Power bank charge calculator
Enter the capacity of the power bank and the device battery, in mAh. The calculator converts them to energy (Wh) and subtracts the losses to get the real number of charges.
How to useHow many charges a power bank gives
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Power bank charge calculator: what it is for
The calculator converts the power bank capacity and the device battery to energy (Wh), using 3.7 V for the power bank cells and 3.85 V for the phone, and applies the overall efficiency you enter (70% by default) to get the real number of charges.
It also shows the real capacity delivered, an estimate of the time per charge based on the charger power, whether the power bank can go in carry-on baggage based on its Wh, and a table with earbuds, a smartwatch, phones and a tablet.
How to use
- Type the power bank capacity and the device battery in mAh.
- Adjust the efficiency and charging power, if you want.
- See how many full charges it gives.
When to use it
- Choosing a power bank capacity before buying.
- Planning trips and hikes.
- Checking whether a power bank can go on a plane.
Frequently asked questions
Why doesn't a 10,000 mAh power bank charge a 4,000 mAh phone 2.5 times?
The mAh of a power bank are measured at the cell voltage, 3.7 V, but the energy comes out at 5 V or more over USB and then goes through the phone's charging circuit. These conversions lose 25% to 40% of the energy; that is why people talk about rated capacity and real capacity.
What efficiency should I use?
Good-quality power banks deliver close to 70% of their rated energy to the device battery, counting all losses. Cheap or old models may be around 60%. Adjust the efficiency field if you know the value for yours.
How do I find my phone's battery capacity?
Search for your phone model with "battery mAh" online or check the manufacturer's specifications. Most current phones have 4,000 to 5,000 mAh.
Can I take a power bank on a plane?
In carry-on baggage, generally yes, up to 100 Wh without approval (about 27,000 mAh at 3.7 V). Between 100 and 160 Wh, the airline must approve it. It is not allowed in checked baggage. The calculator shows the Wh of yours.
Is it really free?
Yes, 100% free. No sign-up, no subscription and no usage limits. All Tools123 tools are free and run right in your browser.