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Watt-hour Calculator

Table of contents

How to use the watt-hour calculatorHow does the mAh to Wh converter work?How to calculate watt-hoursMilliamp hours to watt-hours – an exampleHow to calculate watt hours from timeWhy do we convert amp hours to watt-hours?FAQs

Welcome to our watt-hour calculator, which allows you to convert electric charge in milliamp hours to watt-hours expressing the electrical energy transfer (power) of the system. You can also calculate watt-hours by entering the power of the device and the time period in hours directly.

You will also learn:

  • What is a watt-hour?
  • Why convert amp hours to watt-hours?

How to use the watt-hour calculator

This quick and intuitive watt-hour calculator is a tool that allows you to convert electric charge in milliamp or amp hours to watt-hours describing energy. If you want to further convert watt-hours to joules, you can also try another of our calculators, namely the energy conversion calculator.

To use our tool, you only need to go through a few steps:

  1. Enter the voltage of your appliance.
  2. Input the charge in mAh or Ah.
  3. The mAh to Wh converter will find the energy for you.

You can also convert watts to kilowatt-hours. Just specify:

  1. Power of your device in watts or kilowatts.
  2. Time during which current flows in the system in hours.
  3. The watt-to-hours calculator will find the final result in various units.

How does the mAh to Wh converter work?

Our watt hour calculator allows you to use electric charge in milliamp or amp hours and voltage in volts to calculate the energy in watt-hours or joules. Amp hours – the shortened name of ampere-hour – indicates how much charge can flow through a battery per one hour. More specifically, it is an electric charge in a battery that enables 1 ampere of current to flow for one hour. For standard AA or AAA batteries, you do not need to use amp hours, as their rating is provided in milliampere-hours (mAh).

On the other hand, voltage is expressed in volts (V) and describes the "pressure" that causes electricity to flow within a circuit. The higher voltage means that more electricity can flow in an electric device. If you want to determine what is a watt-hour, it is the total amount of energy generated or consumed over a period of time (an hour) by a system with 1 watt of power generation/consumption. In other words, one watt-hour equals one watt of average power flow over an hour.

How to calculate watt-hours

To calculate the relationship between charge in amp hours and voltage in volts, the formula should be used:

Wh=Ah×V\rm Wh = Ah × V

1 amp hour is equal to 1000 milliamp hours, so if you want to calculate watt-hours from mAh you can simply divide the result by 1000:

Wh=mAh×V/1000\rm Wh = mAh × V / 1000

Milliamp hours to watt-hours – an example

Let's say you have a lithium-ion polymer battery that has 1200 mAh and a nominal voltage of 3.7 V. When we use our converter, we can directly calculate the energy of the battery in watt-hours:

1200 mAh×3.7 V=4.44 Wh\rm 1200\ {mAh} × 3.7\ {V} = 4.44\ {Wh}

In this example, your battery has a capacity of 4.44 Wh. For comparison, laptop batteries have energy output in the range from 22 Wh to nearly 100 Wh, depending on brand and type.

Do you want to know how to calculate the power consumed by your electrical devices? Don't miss our electrical power calculator.

How to calculate watt hours from time

If you want to calculate watt hours over a period of time t in hours, you can simply multiply:

Wh=W×t\mathrm{Wh} = \mathrm{W} \times t

Therefore, one watt over six hours would be six watt-hours of energy. One kilowatt-hour is equal to 1000 watt-hours, so in order to convert watts to kilowatt hours, you need to divide the result by 1000:

kWh=W×t1000\mathrm{kWh} = \frac{\mathrm{W} \times t}{1000}

If you use other units of energy, i.e., mechanical horsepower, try our power converter to convert them into watts.

Why do we convert amp hours to watt-hours?

When we convert amp hours to watt-hours we can better estimate how much energy can be delivered by different batteries. Different types of batteries work at a specific voltage, so comparing them only by amp hours can lead to misleading conclusions.

Sometimes you can conclude that a battery with higher amp hours can provide much more energy, but you should always take into account the nominal voltage at which the battery is operating. Therefore, you can use our converter to calculate electric capacity in watt-hours for each battery and compare them.

💡 Voltage is typically fixed for different types of batteries and depends on type of internal chemistry (alkaline, lead acid, lithium, etc.), while their charge in milliamp hours is printed on the side.


How do I calculate watt hours?

You can determine watt hours in multiple ways.

The first one is by using charge and voltage.

  1. Multiply the charge in amp hours by the voltage in volts.

  2. The result is watt hours.

    Wh = Ah × V

You can use the second method when you are studying energy in terms of power over time.

  1. Multiply the power in watts by the time in hours.

  2. The result is energy in watt hours.

    Wh = W × t

How do you convert Wh to watts?

Converting watt hours to watts is simple and straightforward. We will start with the formula to determine watt-hours:

Energy (Wh) = Power (W) × Time (hrs)

Now, rearrange it to determine watts:

Power = Energy / Time

So, all you have to do is divide the energy in watt-hours by time in hours, and you have the power in watts.

How many amp-hours is 500 watt-hours?

500 watt-hours is 62.5 amp-hours, assuming the voltage is 8 volts (V).

Determining the amp hours from watt hours is reasonably straightforward, especially if you know the voltage. You may use the formula:

Charge = Energy / Voltage

So, you figure out the amp hours, which is the unit of charge, by dividing the watt hours, the energy, by the voltage.

What is 1 watt-hour?

One watt-hour is the amount of energy used by an appliance with a power rating of 1 W that is used for one hour.

For example, suppose you had a 25-watt light bulb in your lamp and kept it on for 4 hours. It would consume 100 watt-hours of energy.

Watt-hours from amp-hours

Watt-hours from time

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