So that you can define  milliamp-hours(mAh) is equal to 1000 times watt-hours(Wh) divided by volts:

How to convert Wh to mAh, How to convert watt-hour (Wh) to milliampere-hour (mAh).

Let’s take an example
Example#1
What is  the electric charge in milliamp-hour(mah) when the energy consumption is 5 watt-hour(Wh)
and the voltage is 10 volts.
Q = 5Wh * 1000/10V = 500mAh

Example#2
Find the electric charge in milliamp-hours when the energy consumption is 2 watt-hours and voltage is 5 volts.the electric charge Q is equal to 1000 times 2 watt-hours, divided by 5 volts:

Q = 1000 * 2Wh/5V = 400

Let’s assume that you know the voltage, you can apply this formula: To go from Wh to mAh, divide Wh by Voltage, and multiply by 1000.

For example:
Energy in watt hour is, E(Wh) = 2 Wh
Voltage is = 3.7 V
Q(mAh) = 1000 x E(Wh) / V = 1000 x 2 / 3.7 = 540.54 mAh
Let’s take One Example, I have a battery with 500mAh battery rated at 10V, then the power(wh) should be 500mAh * 10V / 1000 = 5Wh.
Watt-Hour (Wh):- A unit of electrical energy equal to the power of one watt in use for one hour; often used as a unit of electricity consumption.

Milliampere-Hour (mAh):- An milliamp-hour (mAh) is a unit for measuring electric power over time. (mAh) is often used to describe the total amount of energy, a battery can store at one time. it’s the easiest way to distinguish the capacity of a battery. The higher the mAh, the longer the battery will last.

Volt:- A volt is a unit to measure the force of the electric current.