What this calculator does
Battery charge time works out how long a device takes to charge from its current level to a target level. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaEnergy needed = capacity × (target% − current%) / 100; time = energy needed / (charger power × efficiency)
The inputs explained
| Field | What to enter |
|---|---|
| Battery capacity (Wh) | A number, measured in Wh. Starts at 50. |
| Current charge (%) | A number, measured in %. Starts at 20. |
| Target charge (%) | A number, measured in %. Starts at 100. |
| Charger power (W) | A number, measured in W. Starts at 65. |
| Charging efficiency | A number. Starts at 0.85. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with battery capacity
Every other input is held at the calculator’s starting values while battery capacity varies. Select any row to load that scenario into the calculator.