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Amperage describes the quantity of charge carriers that are being moved passed a point in any given second.

One of the simplest (though not actually the official) definitions of an ampere (amp) is 1 coulomb of charge carriers passing through a given location per second.

One coulomb is equal to 6.242 x 10^18 (6,242,000,000,000,000,000) charge carriers. A fantastically large number, but given the relative size of electrons, one can imagine that number of charges moving on a relatively modest wire. Consider household wiring, which is typically 14 or 12 gauge, and rated at carrying 10 or 15 amps (at 120 volts), respectively.

Common Amperages

60 Watt incandescent light bulb500mA (0.5A)
10 Watt LED (60 Watt incandescent equivalent)~100mA (0.1A)
Hair Dryer12 amps

Amp Hours (Ah)

When describing the quantity of charge either available, or used, amp hours (Ah) are used. An amp hour is an hour's worth of amps, or 3,600 coulombs (since there are 3,600 seconds in an hour).

Amp hours are often expressed in milliampere hours (mAh), which is one-thousandth of an amp hour, or 3.6 coulombs. For reference, a typical AA NiMH rechargeable battery will have ~2500 mAh (2.5Ah), and a D NiMH rechargeable has ~10,000 mAh (10 Ah).

Common Unit Magnitudes

MagnitudeValue in amps
nanoamp (nA)0.000000001A
microamp (µA)0.000001A
milliamp (mA)0.001A
amp (A)1.0A

Further Reading

For a much more in depth discussion regarding amps, see Part 2 of the Electronics Tutorial