What is the difference between Amp hours (Ah) and Watt hours (Wh) of a battery? and how to convert Amp hours (Ah) to Watt hours (Wh)?

On October 5, 2024

Introduction

Converting amp hours (Ah) to watt hours (Wh) is essential when comparing battery capacity and energy, especially for drones, VTOL aircraft, and semi solid state batteries. While Ah measures electrical charge, Wh represents the total usable energy of a battery, making it the correct metric for performance comparison.

Difference Between Ah and Wh

Amp hours (Ah) refers to the amount of the current that can be drawn from a battery in the duration of on hour. So a battery rated at 66Ah can theoretically provide 66 ampere for 1 hour, or 1 ampere of current for 66 hours. You may know ampere hour as the nominal capacity of a battery which is written on its label. So for a 6S 32000mAh solid state battery, the ampere hour or Ah equals its capacity which is 32000mAh.

On the other hand, Watt hour (Wh) is the total stored energy of the battery, which is a combination of the both ampere and voltage. So a more meaningful metric that can be used to compare different models of batteries is to refer to their Wh/kg or their energy density. So for example, a 6S 27000mAh solid state battery has 640Wh energy, while a 12S 27000mAh solid state battery has dual energy of equal to 1280Wh. This may not be a good measure because these two models both have around 272Wh/kg energy density.

How to convert Ah to Wh

The formula to convert Ah to Wh is simple:

Formula:
Quick Answer:
Watt hours (Wh) = Amp hours (Ah) × Battery Voltage (V)

Example:
A 6S 22000mAh (22Ah) ultra-high-voltage solid-state battery with 3.95V/cell nominal voltage:

Total voltage = 6 × 3.95V = 23.7V
Watt hours = 22Ah × 23.7V = 521.4Wh

In order to convert amper hour to watt hour, you need to know the voltage of the battery. And if you multiply the voltage of the battery by its Amp hours, you will get the Watt hours of the battery. For example, for a 6s 22000mAh solid state battery, its amp hour is 22Ah, or in other words, it has 22Ah capacity or electrical charge. Since it is an ultra high voltage model, it would have 3.95v/cell nominal voltage, leading to a total of 6×3.95v=23.7v output voltage. Consequently, the Watt hours of this model would be 22Ah x 23.7v = 521.4Wh.

How to Convert Wh to Ah

To convert Watt hours (Wh) back to Amp hours (Ah), simply divide by the battery voltage:

Formula:
Amp hours (Ah) = Watt hours (Wh) ÷ Battery Voltage (V)

Example:
If a 6S battery has 948Wh of energy and 23.7V nominal voltage:

Ah = 948Wh ÷ 23.7V ≈ 40Ah
This means it is approximately a 6S 40000mAh battery

Inversely, to convert the Watt hour to Amp hour, you should divide the number by voltage of the battery. For example, for a 6S battery, if we know that its Watt hour is 948Wh, by dividing the Wh by the battery’s voltage which 23.7v, we would get 948Wh / 23.7v = 40 Ah. So the Amp hour or capacity of the battery is 40000mAh, and it will be a 6S 40000mAh battery.

You can see a few more examples of conversion between Ah and Wh, as well as the Wh/kg value, for a few different models with different capacities and different numbers of cells:

Sample Ah to Wh Conversion Table

Model	Ampere Hour (Ah)	Watt Hour (Wh)	Energy Density (Wh/kg)
7S 35000mAh battery	35Ah	968Wh	237Wh/kg
14S 44000mAh battery	44Ah	2433Wh	237Wh/kg
18S 66000mAh battery	66Ah	4692Wh	299Wh/kg
24S 66000mAh battery	66Ah	6257Wh	297Wh/kg

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Frequently Asked Questions About Ah and Wh

How do you convert Ah to Wh?

To convert amp hours (Ah) to watt hours (Wh), multiply the battery capacity in Ah by its nominal voltage.
Wh = Ah × Voltage.

Is higher Ah always better than Wh?

No. Ah only measures electrical charge, while Wh measures total energy. Two batteries with the same Ah but different voltages can have very different energy capacities.

Why are watt hours more important for drones and VTOL aircraft?

Flight time and payload performance depend on total energy, not just charge. Watt hours (Wh) provide a more accurate comparison for UAV, multirotor, and VTOL battery selection.