How to Convert mAh to Wh: Formula and Examples

Battery capacity is often listed in milliamp-hours (mAh), especially for phones, power banks, cameras, and other portable electronics. But when you want to compare batteries that operate at different voltages, watt-hours (Wh) are usually more useful.

The conversion is straightforward once you know the battery voltage.

Wh = (mAh × V) ÷ 1,000

The important part is choosing the correct voltage for the calculation.

For a broader explanation of how mAh, Ah, Wh, and voltage fit together, see:

https://medium.com/@volodymyrzh/battery-capacity-explained-mah-wh-amp-hours-decoded-1dc676be5a38

The mAh to Wh Formula

Use this formula:

Watt-hours (Wh) = milliamp-hours (mAh) × voltage (V) ÷ 1,000

The division by 1,000 is necessary because:

1 Ah = 1,000 mAh

For example, imagine a battery rated at:

5,000mAh
3.7V

The calculation is:

5,000 × 3.7 ÷ 1,000 = 18.5Wh

So a 5,000mAh battery rated at 3.7V stores approximately 18.5Wh of nominal energy.

If you need a refresher on what mAh actually measures, see:

https://digitalowl.fika.bar/what-is-mah-milliamp-hours-explained-simply-01M2GD3RKJD95V79BPHEW37S32

Why Voltage Is Required

mAh measures electrical charge. It does not tell you the total amount of energy by itself.

Voltage provides the additional information needed to convert that charge into energy.

Consider two batteries:

Battery A: 10,000mAh at 3.7V
Battery B: 10,000mAh at 7.4V

They have the same mAh rating, but not the same energy capacity.

Battery A:

10,000 × 3.7 ÷ 1,000 = 37Wh

Battery B:

10,000 × 7.4 ÷ 1,000 = 74Wh

Battery B contains roughly twice the nominal energy even though both batteries are labelled 10,000mAh.

This is why mAh should not be compared across different battery voltages without additional context.

For more on the role voltage plays in battery specifications:

https://digitalowl.fika.bar/what-is-voltage-battery-voltage-explained-simply-01M2GH66XEB0MHMG3Z2Y7SNBEE

Which Voltage Should You Use?

This is where many mAh-to-Wh calculations go wrong.

You should normally use the nominal battery voltage associated with the stated mAh capacity.

Suppose a power bank contains lithium-ion cells with a nominal voltage of approximately 3.7V and is advertised as 20,000mAh.

Its nominal stored energy is approximately:

20,000 × 3.7 ÷ 1,000 = 74Wh

Do not automatically use the power bank's 5V USB output voltage.

Calculating:

20,000 × 5 ÷ 1,000 = 100Wh

would only be valid if the 20,000mAh rating itself were specified at 5V. In many conventional power-bank specifications, the advertised mAh figure refers to the internal cell capacity at its nominal cell voltage.

The battery then converts that internal voltage to the USB output voltage, and conversion losses mean the delivered output energy will also be somewhat lower than the theoretical stored energy.

Always check what voltage the manufacturer associates with the stated capacity.

mAh to Wh Conversion Examples

Here are several simple examples.

3,000mAh at 3.7V

3,000 × 3.7 ÷ 1,000 = 11.1Wh

Nominal energy capacity: 11.1Wh

5,000mAh at 3.7V

5,000 × 3.7 ÷ 1,000 = 18.5Wh

Nominal energy capacity: 18.5Wh

10,000mAh at 3.7V

10,000 × 3.7 ÷ 1,000 = 37Wh

Nominal energy capacity: 37Wh

20,000mAh at 3.7V

20,000 × 3.7 ÷ 1,000 = 74Wh

Nominal energy capacity: 74Wh

5,000mAh at 7.4V

5,000 × 7.4 ÷ 1,000 = 37Wh

Notice something important: this battery has only half the mAh rating of a 10,000mAh 3.7V battery, yet both represent approximately 37Wh.

That is exactly why Wh is more useful when comparing batteries with different voltages.

What Does Wh Tell You That mAh Does Not?

Watt-hours express energy rather than charge.

A Wh rating gives you a common basis for comparing different battery systems and is also useful when estimating how long a battery might run a particular load.

For example, two batteries may both be labelled 20,000mAh, but if their nominal voltages differ, their actual stored energy can differ substantially.

Wh makes that difference visible.

For a focused explanation of watt-hours:

https://digitalowl.fika.bar/what-is-a-watt-hour-wh-explained-simply-01M2GM471S7BVV7BQ4R37DEEAP

Does the Formula Give Exact Usable Energy?

Not necessarily.

The formula calculates nominal energy from the stated charge capacity and voltage.

Real usable energy can be lower because of factors such as:

• voltage conversion losses;

• battery-management reserves;

• inverter or electronic losses;

• temperature;

• discharge rate;

• battery age;

• device cutoff limits.

So converting 20,000mAh at 3.7V to 74Wh does not guarantee that a connected device will receive exactly 74Wh.

The calculation is still very useful because it gives you a common nominal energy figure for understanding and comparing batteries.

The Simple Rule

To convert mAh to Wh, remember:

Wh = mAh × V ÷ 1,000

So:

10,000mAh at 3.7V = 37Wh

10,000mAh at 7.4V = 74Wh

The mAh value alone is not enough. You must know the voltage associated with that capacity rating.

Once voltage is included, converting mAh into Wh makes batteries with different electrical configurations much easier to compare.