Phone Charge Time Calculator
Estimate how long a phone takes to charge from empty, from the battery size and the charger's power. Good for choosing a charger or planning overnight charging.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
Battery energy in watt-hours is the milliamp-hours divided by 1000, times the battery voltage. Divide that by the charger's watts, after allowing for the efficiency, to get hours.
Charging slows as the battery nears full, so the last part takes longer than this estimate says. Treat the result as a starting point.
Worked example
A 4,500 mAh phone battery on a 20 W charger, at 80% efficiency, takes about 1 h 4 min 58 s to fill from empty.
Questions
Why does charging slow down?
Phones reduce the power near full to protect the battery. The last fifth or so of the charge can take a long time.
Where do I find the battery size?
It is in the phone's specification sheet, usually in mAh. Some phones list it in watt-hours instead.
What efficiency should I use?
The 80 percent starting value is an assumption. Some of the power is lost as heat in the charger and cable.
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