Device Charging Time Calculator
Free toolEnter the battery capacity, charger power, and current battery percentage to find out the real charging time, accounting for energy lost as heat.
Battery and charger details
Some energy is lost as heat during charging; 85% is a realistic typical value, not 100%.
Estimated time
How to use it
- Enter the battery capacity in mAh and, if you know it, its voltage.
- Set the charger power in watts and the percentage you want to charge.
- Read the estimated charging time.
What it works out and how
First the capacity is turned into energy: watt hours = mAh ÷ 1000 × voltage, with 3.85 V by default, the usual nominal voltage of phone batteries. Then the energy still needed is divided by the charger power times the efficiency, 85% by default. A 5,000 mAh battery holds about 19 Wh and with a 20 W charger takes a little over an hour in theory.
Frequently asked questions
Why does my phone take longer than calculated?
Charging is not constant: from about 80% the phone lowers the power to protect the battery, and the last stretch is the slowest.
Does a more powerful charger always charge faster?
Only up to the maximum the device accepts. A phone that takes 25 W will not charge faster with a 65 W charger.
Does it work for a power bank?
Yes. Enter its capacity and input power. Bear in mind that its usable capacity when charging other devices is lower than the rated one.