Mobile & Electronics

Battery Charge Percentage Calculator

How full a battery is as a percentage, from the charge left in it or the charge taken out.

6 inputs Free, no sign-up

Your figures

What the battery holds when full.

Fill in this or the charge used, not both.

The alternative to the field above - how much has come out since it was full.

Try an example

Result

Your result

Enter your figures and the result appears here.

Estimates only. Rates, fees and specifications change. Confirm against the official source before you rely on a figure — see our disclaimer.

About this calculator

A battery percentage is the charge remaining divided by the charge when full. Straightforward arithmetic, and useful when you are working from measured figures rather than a phone's own display.

It is worth knowing that the two can disagree. A phone's percentage is estimated by its battery management chip from voltage and current, not measured directly — which is why a phone can jump from 20% to 5%, and why an old battery still reports 100% while holding far less than it once did.

How to use this calculator

  1. Enter the battery's full capacity.
  2. Enter either the charge remaining or the charge used — whichever you have. If you give the charge used, the remainder is worked out.
  3. Read the percentage and what is still needed for a full charge.

The formula

Battery level = Remaining / Full capacity x 100
Remaining     = Full capacity - Used

A full capacity of zero has no answer — every reading would be a division by zero — and a remaining charge above the full capacity is refused rather than producing a figure above 100%, because a battery cannot hold more than it holds.

SymbolMeaningUnit
Full Capacity when full mAh
Remaining Charge left in it mAh
Level Percentage full %

Worked example

A 5,000 mAh battery with 1,800 mAh left:

Level = 1800 / 5000 x 100 = 36%
Still needed for full     = 3,200 mAh

Notes and limits

  • This is arithmetic on your figures. A phone's own percentage is an estimate from voltage and current, so the two can differ.
  • A battery's full capacity falls with age. A phone reporting 100% after three years is full relative to what it can now hold, not to what it held when new — which is why battery health, reported separately, matters.
  • Percentage readings are least accurate at the extremes, which is where a phone is most likely to jump several points at once.
  • Charging between about 20% and 80% causes less wear than routinely running a battery flat or filling it completely.

What this calculation assumes

  • The full capacity entered is what the battery holds now, not when it was new.
  • This is arithmetic on your figures rather than a reading from the battery itself.
  • A remaining charge above the full capacity is refused rather than reported above 100%.

Frequently asked questions

How do I calculate battery percentage?

Divide the charge remaining by the full capacity and multiply by 100. A 5,000 mAh battery with 1,800 mAh left is at 36%.

Why does my phone's percentage not match this?

Because a phone estimates its level from voltage and current rather than measuring charge directly. The estimate is least reliable at the top and bottom of the range, which is where sudden jumps happen.

Does 100% mean the same thing on an old battery?

No. It means full relative to what the battery can now hold, which is less than when it was new. That is why phones report battery health as a separate figure.

What is the best range to keep a battery in?

Roughly 20% to 80% causes less wear than routinely emptying or completely filling it. Charge fully when you need the endurance; there is no benefit to doing it every day.

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