7. What Is Watt-Hour & Amp-Hour? (Easy, Simple Definition)


Before you can understand what a watt-hour is, please make sure you read my very short, easy-to-read article: What Is an Electric Circuit?

Then, come back to EASILY understand the bare-bone basics about watts.


To understand what watts are, you must understand what voltage is (measured in volts) and what an electrical current is (measured in amps).

Voltage: Volts

Electricity is caused by the movement of electrons in an electrical circuit.

But the electrons need something to push them along the circuit. This electrical push/pressure is called voltage.

In a circuit, in order to move an electron from one point (negative) of the power source to the other point (positive), you need voltage.

The greater the voltage, the greater the flow of electrons through an electrical conductor.

So, in other words, voltage just measures how strongly electricity is being pushed through a circuit.

Voltage is measured in Volts (V).

Many circuits are designed to only accept a certain number of volts.

Electrical Current: Amps or (A)

The electrical current is the unit of how many electrons move past a given point per second through a conductor.

This current is measured in Amps (A).


Power is measured in Watts.

So when you put volts and amps together, you can tell how much current is flowing and how hard it’s flowing. Multiply these numbers, and you get watts.

Power Formula:


Watts and kilowatts (kilo = 1000) express how much energy is consumed per chunk of time (which is what we call power).

In other words, the wattage gives you a good idea of how much power something is using (like a fridge, lamp, TV, etc) or how much power something is generating (like a solar panel or wind turbine).

Watt-Hour (Wh)

We can use the wattage with time to determine what are called watt-hours (Wh).

Watt-Hour Rating = Wattage x Hours

You probably saw that your electric bill is in kilowatt-hour (KWh).

If you multiply a kilowatt (1000 watts) by an hour, then you can see how much energy that you consumed by running your fridge, computer, TV, lights, and other appliances in your home.

In other words, if you used 1000 watts for 1 hour, then you used 1000 watt-hours (or 1 kilowatt-hour).

Amp-Hour (Ah)

Watt-hour is really good to understand how much electricity an appliance is using or a solar power system is generating. But watt-hour is also good to determine how much electricity a battery can store.

But you’ll usually only see amp-hour (Ah) and volt prominently marked on a battery’s label. Amp-hour, just like watt-hour, is when we use amps with time to determine amp-hours.

Amp-Hour (Ah) = Amperage x Hours

Let’s say we have a typical 12-volt battery and on the label it says that it can produce 100 amp-hours (100Ah). In other words, this battery will be able to give you 100 amps for 1 hour at 12 volts.

If you multiply 12 volts and 100 amp-hours, you’ll get 1200 watt-hours.

Watt-Hour = Volts x Amp-Hour

And then it’s easy for you to figure out that this 1200 watt-hour battery can power a 100-watt appliance for 12 hours.

The watt-hour is really the best way to compare 2 batteries. When you know the watt-hour rating of a battery, you can determine how long it can power your appliances for and how long it will take to recharge the battery with something like a solar or wind power system, or an AC charger.

Other Basic Electricity Fundamentals…

  1. What Is an Electric Circuit?
  2. What Is an Electric Current (Amps)?
  3. What Is Voltage (Volts)?
  4. What Is Electrical Resistance?
  5. What’s the Difference Between AC and DC?
  6. What Are Watts?
  7. What Is Watt-Hour & Amp-Hour?