How to get accurate numbers
Each calculator works from the numbers you enter, so the result is only as good as those numbers. The design capacity is the rated mAh on your phone's specification page or on the battery itself. The current full charge capacity is harder to know: Android does not show it on most phones, and the percentage on your screen is an estimate that drifts as the battery ages.
The most reliable way to measure it is to watch how many mAh go into the battery during a partial charge, ideally from about 20% to 80%, where the charge level reading is most stable. The battery health calculator has a mode for exactly that: enter the mAh added and the start and end percentages, and it works out the full capacity for you.
Which tool to use
- Charging time calculator: planning a quick top-up before you leave, or checking whether a new charger is as fast as it claims.
- Battery health calculator: deciding whether a battery is worn enough to replace, or comparing two phones before you buy a used one.
- Battery life calculator: estimating how long a charge lasts for streaming, navigation or a long day away from a charger.
All three run entirely in your browser. Nothing you type is sent anywhere, and you do not need an account.