# Ampere hour

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An ampere hour or amp hour (symbol: A⋅h or A h; often also unofficially denoted as Ah) is a unit of electric charge, having dimensions of electric current multiplied by time, equal to the charge transferred by a steady current of one ampere flowing for one hour, or 3,600 coulombs.[1][2]

Ampere hour
Rechargeable batteries
Top: AA battery (2500 mA⋅h)
Bottom: AAA battery (1000 mA⋅h)
General information
Unit systemNon-SI metric unit
Unit ofElectric charge
SymbolA⋅h
Conversions
1 A⋅h in ...... is equal to ...
SI units   3600 C
Electrostatic units   1.079253×1013 statC
Electromagnetic units   360 abC
Gaussian units   1.079253×1013 Fr

The commonly seen milliampere hour (symbol: mA⋅h, mA h, or unofficially mAh) is one-thousandth of an ampere hour (3.6 coulombs).

## Use

The ampere hour is frequently used in measurements of electrochemical systems such as electroplating and for battery capacity where the commonly known nominal voltage is dropped.

A milliampere second (mA⋅s) is a unit of measure used in X-ray imaging, diagnostic imaging, and radiation therapy. It is equivalent to a millicoulomb. This quantity is proportional to the total X-ray energy produced by a given X-ray tube operated at a particular voltage.[3] The same total dose can be delivered in different time periods depending on the X-ray tube current.

To help express energy, computation over charge values in ampere hour requires precise data of voltage: in a battery system, for example, accurate calculation of the energy delivered requires integration of the power delivered (product of instantaneous voltage and instantaneous current) over the discharge interval.[4] Generally, the battery voltage varies during discharge; an average value or nominal value may be used to approximate the integration of power.[5]

## Other measures of electric charge

The Faraday constant is the charge on one mole of electrons, approximately equal to 26.8 ampere hours. It is also used in electrochemical calculations.

## Examples

• An AA size dry cell has a capacity of about 2 to 3 ampere hours.
• An average smartphone battery usually has between 2,500 and 4,000 milliampere hours of electric capacity.
• Automotive car batteries vary in capacity but a large automobile propelled by an internal combustion engine would have about a 50 ampere hour battery capacity.
• Since one ampere hour can produce 0.336 grams of aluminium from molten aluminium chloride, producing a ton of aluminium requires transfer of at least 2.98 million ampere hours.[6]