How to convert amp hours to kilowatt hours

Written by mark stansberry
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How to convert amp hours to kilowatt hours
Power lines transport electrical energy. (electricity image by brelsbil from

Converting amp hours to kilowatt hours is often necessary if you want to compare the amount of power you can obtain from different energy generation devices, such as wind, hydro power and solar energy generators, and energy storage devices, such as batteries. It's a simple process to convert amp hours to kilowatt hours; a few arithmetic operations and you're done.

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  1. 1

    Obtain the amp-hour rating of your energy generation or energy storage device. A boat battery, for example, may list a 0.8 amp-hour rating. This rating could be listed on the side of the product, or in the owner's manual. Instead of amp hours, the rating also could be listed in milliampere hours, often abbreviated mAHr.

    To convert milliampere hours to amp hours, divide the milliampere-hour rating by 1,000. For example, If a battery is rated at 3,500 milliampere hours, the amp-hour rating would be 3.5 amp hours, since 3,500 divided by 1,000 is 3.5.

  2. 2

    Determine the operating voltage of your energy generation or energy storage device. Batteries are also given a voltage rating, often listed right on the side. Common voltage ratings for batteries include 3.3 volts, 5 volts and 12 volts. To determine exactly the voltage level of your battery, the best approach is to measure the voltage across the battery. The battery, if not fully charged, could have a lower voltage level than what is indicated on the battery.

  3. 3

    Calculate the watt-hour rating. Multiply the amp-hour rating by the voltage rating. If you have a battery that has a 0.8 amp-hour rating, and the battery has a voltage rating of 12 volts, the watt-hour rating would be 9.6 watt hours, since 12 times 0.8 is 9.6.

    In other words, the battery could power a device that requires 9.6 watts for one hour. Likewise, if you had a battery with a 0.8 amp-hour rating, it could power a 0.8-amp device for one hour.

    Watts formula, a formula to compute power, states that the power in satts is equal to the current multiplied by the voltage. If a device requires 3 amps of curent and the battery that it uses is a 30-volt battery, the power the device uses is 90 watts, since 3 times 30 is 90.

    The formula for watt hours is an extension of watts formula. It states that watt hours is equal to amp-hours multiplied by the voltage across the device.

  4. 4

    Calculate the kilowatt-hour rating. One kilowatt hour equals one thousand watt hours. Convert watt hours to kilowatt hours by dividing the watt-hour rating by 1,000. For a 9.6 watt-hour rating, the kilowatt-hour rating would be 0.0096 kilowatt hours, since 9.6 divided by 1,000 is 0.0096.

Tips and warnings

  • Very powerful and dangerous batteries will often be rated in kiloamperes. A kiloampere is equivalent to 1,000 amperes (amps). To convert kiloampere hours to amp hours, multiply the kiloampere-hour rating by 1,000. For example, if battery is rated at 3 kiloamp, it will have an amp-hour rating of 3,000 amp hours, since 3 multiplied by a 1,000 is 3,000.

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