Mobile & Electronics

mAh to Wh Calculator

Convert a battery's mAh into watt-hours - the figure that lets you compare two batteries honestly.

4 inputs Free, no sign-up

Your figures

The figure printed on the battery or in the specifications.

From the battery label. Single-cell lithium packs are usually marked 3.7 V or 3.85 V nominal; laptop and tool packs are higher. This is not assumed for you, because it changes the answer proportionally.

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

mAh is not a measure of energy, and comparing two batteries on it alone is the commonest mistake in this subject. A 10,000 mAh pack at 3.7 V holds 37 Wh. A 10,000 mAh pack at 7.4 V holds 74 Wh — twice as much, from an identical-looking number.

Watt-hours is the figure that compares. It is also the figure airlines use, which is why a power bank's Wh rating is the one printed in the small text.

How to use this calculator

  1. Enter the capacity, choosing mAh or Ah.
  2. Enter the battery's nominal voltage from its label. It is not assumed, because it scales the answer directly.
  3. Read the watt-hours. That is the figure to compare against another battery.

The formula

Wh = mAh x V / 1000
Wh = Ah x V

Capacity in mAh measures charge — how many electrons the battery can move. Energy is charge multiplied by the voltage it moves at. Two batteries holding the same charge at different voltages hold different amounts of energy, which is why the voltage cannot be left out.

A power bank's cells are usually around 3.6–3.7 V nominal, and its case is labelled with the cell capacity rather than the 5 V output capacity. That is why a 10,000 mAh power bank never delivers 10,000 mAh to a phone: the energy is stepped up to 5 V, and 37 Wh at 5 V is about 7,400 mAh before any losses.

SymbolMeaningUnit
mAh Charge the battery holds mAh
V Nominal voltage V
Wh Energy the battery holds Wh

Worked example

A phone battery, 5,000 mAh at 3.7 V:

Wh = 5000 x 3.7 / 1000 = 18.5 Wh

A 10,000 mAh power bank at 3.7 V:

Wh = 10000 x 3.7 / 1000 = 37 Wh

Both are well under the 100 Wh limit airlines generally apply to cabin baggage.

Notes and limits

  • Always compare batteries on watt-hours, never on mAh alone, unless you already know both are at the same voltage.
  • The voltage on a battery label is the nominal figure — an average over the discharge. The actual voltage starts higher and ends lower.
  • A power bank's mAh is its cell capacity, not what it can deliver at 5 V. Converting to Wh first is how you find what it can actually give a phone.
  • Airlines limit lithium batteries by watt-hours, commonly 100 Wh without approval. That is why the Wh figure is on the case.
  • For what a pack actually delivers after conversion losses, use the power bank energy calculator.

What this calculation assumes

  • The voltage entered is the battery's nominal voltage, taken from its label.
  • This is the nominal energy the battery holds, before any conversion losses.
  • No cell chemistry or voltage is assumed on your behalf.

Frequently asked questions

How do I convert mAh to Wh?

Multiply the mAh by the voltage and divide by 1,000. A 5,000 mAh battery at 3.7 V is 18.5 Wh.

Why do I need the voltage?

Because mAh measures charge, not energy. Energy is charge times voltage, so two packs with the same mAh at different voltages hold different amounts of energy - a 7.4 V pack holds twice what a 3.7 V one does.

What voltage should I use for a phone battery?

Whatever is printed on it. Single-cell lithium phone batteries are usually marked 3.7 V or 3.85 V nominal. This page does not fill it in for you, because the two differ by 4% and the label is right there.

Why does my 10,000 mAh power bank not give my phone 10,000 mAh?

Because the power bank's cells are at about 3.7 V and its output is 5 V. Converting energy from one voltage to the other loses some as heat, and the 5 V figure is lower to begin with. Expect roughly 6,000 to 6,500 mAh at 5 V from a 10,000 mAh pack.

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