Watts to Amp Hours

It should not come as a surprise when you see the terms watt and amp when dealing about electricity and batteries.

While they are both considered as units of measurements, they do not actually mean the same thing. Watts (W) measure the rate at which energy is transferred and Amperes (A) measure the amount of electric current flowing through a circuit.

Having knowledge about watts and amps is a great advantage especially to those who use batteries for their power needs so they can make the right decision when it comes to buying the battery for their power requirements.

Let’s find out below just how watts and amps are related to each other and how we can convert one to the other.

Watt-Hour Explained

A watt-hour (Wh) is a unit of energy commonly used in electrical applications. It measures the capacity of power (watts) moving over time (one hour). In batteries, this would mean the number of watts that an appliance utilizes per hour.

For example, if an electric appliance has a rating of 100W, it will use 100Wh of power in an hour and if you extend it up to three hours, it will consume a total of 300Wh. Having said that, if you have three electric gadgets that are all rated at 100W, running all of them at the same time for an hour will consume 300Wh in total.

Remember this formula: total number of watts x total number of hours = watt-hours 

Let’s have another example. Let’s say you have an 85W LED television and you would like to know how many watts it uses in 5 hours, your equation would show 85 watts x 5 hours = 425 watt-hours / 425Wh. This means that watching for 5 hours on your tv would use a total of 425Wh of electricity.

Amp-Hour Explained

Now that we know what a watt-hour is, let’s define another electricity concept which is the amp-hour. 

An amp-hour (also known as ampere-hour / Ah) is a unit of electric charge, usually used for batteries, which tells you how many amps the battery can deliver in an hour. It is important to take note that amp-hours is actually not a measurement of energy, but rather a measurement of charge.

A 100Ah battery would then mean that it can supply a load of 100 amperes in an hour. Using this battery on a 25 ampere electronic device, the device can then run for a total of 4 hours (100/25=4) assuming the battery operates at 100% efficiency.

Let’s Convert: Amp Hours to Watt Hours

What do you need to do if you have a 200Ah battery and you would like to know its capacity in watt-hour / Wh? 

Remember this formula: amp hours x voltage = watt hours

Assuming that your 200 amp hour (200Ah) battery is powered by a 12 volt system (12V), your equation would be 200Ah hours multiplied by 12V, your battery then has a capacity of 2400 watt hours (2400Wh).

Just to reiterate that amp hours is not equal to energy, you could actually get the same 2400Wh from a 100Ah battery with a 24V system. The equation then would look like this: 100Ah x 24V = 2400Wh.

Here are some other examples of converting amp hours to watt hours:

• 20 Ah battery x 12v = 240Wh
• 50 Ah battery x 24v = 1200Wh
• 100 Ah battery x 48v = 4800Wh

Let’s Convert: Watt Hours to Amp Hours

Now, if you find yourself on the other side where you need to find out how many amp hours (Ah) your electrical system can handle, there is also a solution to this. 

Remember this formula: watt hours / voltage = amp hours

Let’s take a look at this example. You have a 240 watt-hour battery that runs on a 12 volt system. To find out its amp hours, you simply need to divide 240 watt hours by 12 volts. This will then give you an answer of 20 amp hours. Easy, right?

Here are some other examples of converting watt hours to amp hours:

• 360Wh / 12v = 30 Ah
• 1200Wh / 24v = 50 Ah
• 4800Wh / 48v = 100 Ah

How Many Watt Hours are there in a 100Ah LiFePO4 Battery?

To make this more realistic, let us use an actual battery called Eco-Intelligent Li from Nature’s Generator, one of the leading brands when it comes to whole house solar generators. 

The Eco-Intelligent Li is a lithium iron phosphate (LiFePO4 / LFP) battery that has a rated capacity of 100Ah and a rated voltage of 48V.

Using the formula above, 100Ah x 48V = watt hours, its battery capacity is a whopping 4800Wh.

Importance of Knowing How to Convert Watts to Amp Hours and Vice-Versa

Using the formula to calculate the amp hours of the battery that you need will help you decide on the right type of battery capacity for your device. This will ensure that you have enough juice to run your device for the desired amount of time.

Knowing the amp hours of your battery and the power specifications of your electric appliance, you can use the formula to calculate the amount of time the battery will last. This is very helpful especially to those who use solar power systems and other appliances where you need to know how long the battery will last before it needs recharging.

If you feel that your battery is not lasting like it’s supposed to, you can use the formula to calculate the amp hours of the battery then compare it to the actual amount of time before the battery gets drained to see if it has decreased. If the answer is yes, chances are your battery has a problem.

Reasons Why People Make Watt-Hour and Amp-Hour Calculations

The most important reason why people make these calculations is so they can understand the energy capacity of their batteries. If you know your battery’s energy capacity, you would also know which device or appliance it can power and how long it will last. 

This kind of knowledge is crucial especially to people who rely on batteries as their source of energy. People who live off the grid and harness energy from the sun via solar panels or from the wind via wind turbines most likely store energy in batteries. People who have backup power systems such as solar generators also rely on batteries. Knowing how to compute the working hours of their batteries before they get fully drained will allow them to choose and use the right devices and appliances for their household.

Final Thoughts

Understanding the relation between amp hours and watt hours will help you understand battery energy capacities. While you can easily find conversion charts online, knowing how to compute watt hours and amp hours on your own will give you the advantage of determining how much energy those batteries will provide you and for how long without relying on the internet.

* We want to give credit where credit is due. Professional writer, Ann Matthew, contributed research and content to this blog titled: Watts to Amp Hours Thank you, Ann, for your contributions!