Use our calculator to easily convert watt hours to milliamp hours (Wh to mAh).
Or would you rather convert milliamp hours to watt hours?
Watt Hours to Milliamp Hours Conversion Chart
Here's a conversion chart converting watt hours to milliamp hours at 3.7V, the most common voltage for small devices such as phones, tablets, headphones, battery packs, and Bluetooth speakers.
|Watt Hours (Wh)||Voltage (V)||Milliamp Hours (mAh)|
How to Convert Watt Hours to Milliamp Hours (Wh to mAh)
To convert watt hours to milliamp hours, divide watt hours by volts and then multiply by 1,000.
Formula: milliamp hours = watt hours ÷ volts × 1,000
Abbreviated formula: mAh = Wh ÷ V × 1,000
I was recently gifted this Bluetooth speaker.
In the spec sheet, it says the battery is a 3.7V 2.775Wh Li-ion battery. To convert the battery's watt hours to milliamp hours, you do the following calculation:
2.775Wh ÷ 3.7V × 1,000 = 750mAh
So my Bluetooth speaker has a battery capacity of 750mAh.
Why Convert Watt Hours to Milliamp Hours?
Calculating a battery's milliamp hours is particularly helpful when deciding on how fast you want to charge the battery. Charging or discharging batteries too quickly can accelerate aging.
For example, let's say you have a 3.7V 18.5Wh portable battery pack. You want to buy a charger that will charge it quickly, but not so quickly that it damages the battery. Unfortunately, your battery pack's product manual gives no guidance on the recommended max charge rate, so you have to figure it out yourself.
To figure out the max number of milliamps your battery charger should output, you first need to convert your battery pack's watt hours to milliamp hours.
18.5Wh ÷ 3.7V × 1,000 = 5,000mAh
So you know you're working with a 5,000mAh battery pack. Next, you need to know the battery's recommended C-rate, which varies based on battery type.
The spec sheet says that the battery is a lithium polymer (LiPo) battery. You do some research and learn that most LiPo batteries have a recommended max charge rate of 1C.
This means the max charge rate of your 5,000mAh battery pack is 5,000 milliamps, or 5 amps. Now you can go out and buy a battery charger with a max charge rate of 5 amps or less, such as this Anker wall charger.
Converting watt hours to milliamp hours can also help you estimate your battery's charge time if you know your charging current in amps or milliamps. You can estimate how long it will take for your 5A (5,000mA) charger to charge your 5,000mAh battery pack by dividing the milliamp hour capacity by the charge current in milliamps.
5,000mAh ÷ 5,000mA = 1 hr
It'll take your charger about an hour to fully charge your battery. Though it's best to treat this as a very rough estimate, because in reality there are many more factors that affect charging speed.
You can also use milliamp hours to estimate your battery's runtime if you know the device's current draw in amps or milliamps. Estimate how long your 5,000mAh battery pack will last powering a 1A (1,000mA) device by dividing its milliamp hour capacity by the device's current draw in milliamps.
5,000mAh ÷ 1,000mA = 5 hrs
So you can expect your battery pack to power the device for about 5 hours before needing to be recharged. As before, this result is best treated as a rough estimate.
How to Convert Milliamp Hours to Watt Hours (mAh to Wh)
Oftentimes, you'll know your device's battery capacity in milliamp hours and you'll need to convert this value to watt hours.
To convert milliamp hours to watt hours, multiply milliamp hours by volts then divide by 1,000.
Formula: watt hours = milliamp hours × volts ÷ 1,000
Abbreviated formula: Wh = mAh × V ÷ 1,000
Let’s say your smartphone has a 3.7V 4,500mAh battery. What is its battery capacity in watt hours?
Plug in its battery voltage and milliamp hours to the above formula to find out.
4,500mAh × 3.7V ÷ 1,000 = 16.65Wh
When expressed in watt hours, your phone has a 16.65Wh battery.
How to Convert Watt Hours to Amp Hours (Wh to Ah)
Larger batteries, such as car batteries or LiFePO4 batteries, more commonly express their battery capacity in amp hours. To convert watt hours to amp hours, you just divide the battery's watt hours by its voltage.
Formula: amp hours = watt hours ÷ volts
Abbreviated formula: Ah = Wh ÷ V
Calculator: Watt Hours to Amp Hours Calculator
Let's say you have a 293Wh solar generator. You look through the spec sheet and find out that its battery voltage is 14.4 volts.
Here's how you convert its watt hours to amp hours:
293Wh ÷ 14.4V = 20.35Ah
Turns out your solar generator has a 20.35 amp hour battery.
How to Convert Kilowatt Hours to Milliamp Hours (kWh to mAh)
Some batteries are so large that their watt hours can be expressed in kilowatt hours. Kilowatt hours are also the units used on your home power bill to convey energy usage. 1 kilowatt hour (kWh) is equal to 1,000 watt hours, like how 1 kilometer is equal to 1,000 meters.
To convert kilowatt hours to milliamp hours, divide kilowatt hours by volts and then multiply by 1 million.
Formula: milliamp hours = kilowatt hours ÷ volts × 1,000,000
Abbreviated formula: mAh = kWh ÷ V × 1,000,000
Let's say you have a 12V 0.75kWh battery. Here's how you'd calculate its milliamp hours.
0.75kWh ÷ 12V × 1,000,000 = 62,500mAh
Your battery has a capacity of 62,500mAh. When converting from kWh to mAh, the resulting number of milliamp hours is often so large that it's easier to express it in amp hours.
Converting milliamp hours to amp hours is as simple as dividing by 1,000. So, in this example, you could also express your battery capacity as 62.5Ah.