Mobile & Electronics

Wh to mAh Calculator

Convert watt-hours back into mAh at a stated voltage - the conversion for reading a laptop battery in phone-battery terms.

4 inputs Free, no sign-up

Your figures

The Wh figure from the battery or the power bank's small print.

The voltage the mAh figure should be quoted at. Change it to 5 V to see what a power bank could deliver over USB.

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 capacity in mAh only means something at a stated voltage. 37 Wh is 10,000 mAh at 3.7 V and 7,400 mAh at 5 V — the same battery, two different numbers, because mAh measures charge rather than energy.

That is exactly why this conversion is useful: it shows what a pack rated in watt-hours would be if it were labelled the way phone batteries are, and what it could theoretically deliver at USB voltage.

How to use this calculator

  1. Enter the energy in watt-hours. Laptop batteries and power bank small print both use it.
  2. Enter the voltage you want the capacity quoted at — the cell voltage for a like-for-like comparison, or 5 V to see the USB-side figure.
  3. Read the mAh.

The formula

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

Choosing the voltage is choosing what the answer means. At the cell voltage you get the number that would be printed on the pack; at 5 V you get the theoretical USB-side capacity before any conversion losses, which is always the smaller figure.

SymbolMeaningUnit
Wh Energy the battery holds Wh
V Voltage to quote at V
mAh Capacity at that voltage mAh

Worked example

A 37 Wh power bank, quoted at its 3.7 V cell voltage:

mAh = 37 x 1000 / 3.7 = 10,000 mAh

The same pack quoted at 5 V:

mAh = 37 x 1000 / 5 = 7,400 mAh

And that 7,400 is before conversion losses. What actually reaches a phone is lower again.

Notes and limits

  • The voltage decides what the answer means. Without stating it, an mAh figure is not comparable to anything.
  • A power bank labelled 10,000 mAh is quoting its cells. At 5 V the same energy is about 7,400 mAh, and after losses closer to 6,000–6,500.
  • Laptop batteries are labelled in Wh precisely because it avoids this ambiguity, their packs being several cells in series.
  • Airlines limit by watt-hours, so for travel the Wh figure is the one that matters and this conversion is not needed.

What this calculation assumes

  • The capacity produced is at the voltage you chose, and means nothing without it.
  • This is a conversion of nominal energy; no conversion losses are applied.
  • No voltage is assumed on your behalf.

Frequently asked questions

How do I convert Wh to mAh?

Multiply the watt-hours by 1,000 and divide by the voltage. 37 Wh at 3.7 V is 10,000 mAh.

Which voltage should I use?

The cell voltage if you want the number that would be printed on the pack, or 5 V if you want to know what it could deliver over USB. They give very different answers, which is the point.

Why is my laptop battery labelled in Wh and my phone in mAh?

Because a laptop pack is several cells in series at a higher voltage, where an mAh figure without the voltage would be meaningless. Phone batteries are single cells at a known voltage, so the convention stuck.

Does this tell me how many times it will charge my phone?

Not on its own, because it does not account for conversion losses. Use the power bank backup calculator, which applies an efficiency you can set.

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