# Ampere hour

(Redirected from MAh)

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 2.5 to 4 ampere 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]

## References

1. ^ "electric charge (Symbol Q). IEV 113-02-10". electropedia.org. International Electrotechnical Commission (IEC). 2020. Retrieved 2020-09-20. Note 7 to entry: The coherent SI unit of electric charge is coulomb, C. The unit ampere hour is used for electrolytic devices, such as storage batteries: 1 A·h = 3,6 kC.
2. ^ Thompson, Ambler; Taylor, Barry N. (2008). Guide for the Use of the International System of Units (SI). NIST Special Publication 811 (PDF) (2nd ed.). Gaithersburg: National Institute of Standards and Technology. p. 45. To convert from ampere hour (A·h) ... to coulomb (C) ... Multiply by 3.6 E+03
3. ^
4. ^ Efty Abir, Najrul Islam (2016). "How to Calculate Amp Hours – Learn of Convert Watts to Amps". Leo Evans. Retrieved 8 December 2016.
5. ^ National Research Council (U.S.) (2004). Meeting the energy needs of future warriors. National Academies Press. p. 27. ISBN 0-309-09261-2.
6. ^ T. L. Brown, H. E. Lemay Jr, "Chemistry the Central Science", Prentice-Hall, 1977 ISBN 0-13-128769-9 page 562