Battery Life Calculator

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mah to wh

mAh to Wh: converter and formula

Open the mAh, Wh and Ah tab, type the capacity and the voltage and read all four units at once. The chemistry shortcut fills in the nominal voltage per cell, and the output voltage field shows how many mAh the same energy is worth at another voltage.

Why mAh alone is not energy

The milliamp-hour measures electric charge, how much current the battery delivers over time. Energy is charge times voltage, so the conversion needs the volts: Wh = mAh x V / 1000. Two 5000 mAh batteries hold different energy if their voltage differs: a 3.7 V cell holds 18.5 Wh, and a 7.4 V pack with the same 5000 mAh holds 37 Wh. Comparing mAh between devices of different voltages misleads.
In power banks the advertised capacity comes from the cell, usually at 3.7 V, while the output is 5 V or more. A 20,000 mAh power bank at 3.7 V holds 74 Wh. At a 5 V output, the same energy corresponds to 14,800 mAh, even with no converter loss at all. That is why the device delivers fewer mAh at the port than the box advertises. Real converter losses cut this further, and they depend on the model.
The nominal voltage by chemistry comes from the Comparison of commercial battery types table: 3.7 V for LCO lithium-ion, 3.6 V for NMC, 3.2 V for LiFePO4, 1.2 V for NiMH, 1.5 V for alkaline and 2.1 V per cell for lead-acid. The real voltage varies with charge, higher when full and lower when nearly empty, so the result is nominal energy, not a measurement.

Checked conversions

20000 mAh power bank at 3.7 V

Input: 20000 mAh, 3,7 V
Expected output: 74 Wh

20,000 x 3.7 / 1,000.

5000 mAh phone battery at 3.7 V

Input: 5000 mAh, 3,7 V
Expected output: 18,5 Wh

One fifth of a 25,000 mAh power bank at the same voltage.

3000 mAh cell at 3.6 V

Input: 3000 mAh, 3,6 V
Expected output: 10,8 Wh

Nominal voltage of NMC lithium-ion.

12 V, 100 Ah battery

Input: 100 Ah, 12 V
Expected output: 1.200 Wh

Or 1.2 kWh, or 100,000 mAh.

74 Wh seen at 5 V

Input: 74 Wh, 5 V
Expected output: 14.800 mAh

Before converter losses.

Full tool FAQ

How do I convert mAh to Wh?

Multiply the mAh by the voltage in volts and divide by 1,000. A 20,000 mAh power bank at 3.7 V holds 20,000 x 3.7 / 1,000 = 74 Wh. To go back, Wh x 1,000 / V.

How long does a 12 V, 100 Ah battery last?

What are efficiency and depth of discharge here?

Why does a power bank deliver fewer mAh than advertised?

How do I estimate the runtime of a UPS?

What is the Wh limit for carrying batteries on a plane?

How do I calculate a series and parallel cell pack?

Does the calculator consider temperature, ageing and the Peukert effect?

How do I size a battery for a load and a runtime?

Does my data leave the browser?

Frequently asked questions

Which voltage do I use for a power bank?

The internal cell voltage, usually 3.7 V, because that is where the maker measures the mAh. The 5 V output serves only to compare what comes out of the port. If the box states the Wh, use that number directly.

How do I convert Ah to Wh?

Multiply the Ah by the voltage. It is the same math as mAh, just without dividing by 1,000: a 7 Ah battery at 12 V holds 84 Wh.

And from Wh to mAh?

Multiply the Wh by 1,000 and divide by the voltage. A 37 Wh battery at 3.7 V is worth 10,000 mAh, and the same energy at 5 V is worth 7,400 mAh.

Next steps

Why mAh alone is not energy

The milliamp-hour measures electric charge, how much current the battery delivers over time. Energy is charge times voltage, so the conversion needs the volts: Wh = mAh x V / 1000. Two 5000 mAh batteries hold different energy if their voltage differs: a 3.7 V cell holds 18.5 Wh, and a 7.4 V pack with the same 5000 mAh holds 37 Wh. Comparing mAh between devices of different voltages misleads.

In power banks the advertised capacity comes from the cell, usually at 3.7 V, while the output is 5 V or more. A 20,000 mAh power bank at 3.7 V holds 74 Wh. At a 5 V output, the same energy corresponds to 14,800 mAh, even with no converter loss at all. That is why the device delivers fewer mAh at the port than the box advertises. Real converter losses cut this further, and they depend on the model.

The nominal voltage by chemistry comes from the Comparison of commercial battery types table: 3.7 V for LCO lithium-ion, 3.6 V for NMC, 3.2 V for LiFePO4, 1.2 V for NiMH, 1.5 V for alkaline and 2.1 V per cell for lead-acid. The real voltage varies with charge, higher when full and lower when nearly empty, so the result is nominal energy, not a measurement.

Checked conversions

20000 mAh power bank at 3.7 V

Input: 20000 mAh, 3,7 V
Expected output: 74 Wh

20,000 x 3.7 / 1,000.

5000 mAh phone battery at 3.7 V

Input: 5000 mAh, 3,7 V
Expected output: 18,5 Wh

One fifth of a 25,000 mAh power bank at the same voltage.

3000 mAh cell at 3.6 V

Input: 3000 mAh, 3,6 V
Expected output: 10,8 Wh

Nominal voltage of NMC lithium-ion.

12 V, 100 Ah battery

Input: 100 Ah, 12 V
Expected output: 1.200 Wh

Or 1.2 kWh, or 100,000 mAh.

74 Wh seen at 5 V

Input: 74 Wh, 5 V
Expected output: 14.800 mAh

Before converter losses.

Full tool FAQ

How do I convert mAh to Wh?

Multiply the mAh by the voltage in volts and divide by 1,000. A 20,000 mAh power bank at 3.7 V holds 20,000 x 3.7 / 1,000 = 74 Wh. To go back, Wh x 1,000 / V.

How long does a 12 V, 100 Ah battery last?

What are efficiency and depth of discharge here?

Why does a power bank deliver fewer mAh than advertised?

How do I estimate the runtime of a UPS?

What is the Wh limit for carrying batteries on a plane?

How do I calculate a series and parallel cell pack?

Does the calculator consider temperature, ageing and the Peukert effect?

How do I size a battery for a load and a runtime?

Does my data leave the browser?

Frequently asked questions

Which voltage do I use for a power bank?

How do I convert Ah to Wh?

Multiply the Ah by the voltage. It is the same math as mAh, just without dividing by 1,000: a 7 Ah battery at 12 V holds 84 Wh.

And from Wh to mAh?

Multiply the Wh by 1,000 and divide by the voltage. A 37 Wh battery at 3.7 V is worth 10,000 mAh, and the same energy at 5 V is worth 7,400 mAh.