The farad (symbol: F) is the unit of electrical capacitance, the ability of a body to store an electrical charge, in the International System of Units (SI), equivalent to 1 coulomb per volt (C/V).

The capacitance of a capacitor is one farad when one coulomb of charge changes the potential between the plates by one volt.

[1][2] Equally, one farad can be described as the capacitance which stores a one-coulomb charge across a potential difference of one volt.

where F = farad, s = second, C = coulomb, V = volt, W = watt, J = joule, N = newton, Ω = ohm, Hz = Hertz, S = siemens, H = henry, A = ampere.

[4] The term "farad" was originally coined by Latimer Clark and Charles Bright in 1861,[5] in honor of Michael Faraday, for a unit of quantity of charge, and by 1873, the farad had become a unit of capacitance.

[6] In 1881, at the International Congress of Electricians in Paris, the name farad was officially used for the unit of electrical capacitance.

Values of capacitors are usually specified in terms of SI prefixes of farads (F), microfarads (μF), nanofarads (nF) and picofarads (pF).

Parasitic capacitance in high-performance integrated circuits can be measured in femtofarads (1 fF = 0.001 pF = 10−15 F), while high-performance test equipment can detect changes in capacitance on the order of tens of attofarads (1 aF = 10−18 F).

[11] A value of 0.1 pF is about the smallest available in capacitors for general use in electronic design, since smaller ones would be dominated by the parasitic capacitances of other components, wiring or printed circuit boards.

Capacitance values of 1 pF or lower can be achieved by twisting two short lengths of insulated wire together.

[12][13] The capacitance of the Earth's ionosphere with respect to the ground is calculated to be about 1 F.[14] The picofarad (pF) is sometimes colloquially pronounced as "puff" or "pic", as in "a ten-puff capacitor".

[15] Similarly, "mic" (pronounced "mike") is sometimes used informally to signify microfarads.

In texts prior to 1960, and on capacitor packages until more recently, "microfarad(s)" was abbreviated "mf" or "MFD" rather than the modern "μF".

A 1940 Radio Shack catalog listed every capacitor's rating in "Mfd.

[16] "Micromicrofarad" or "micro-microfarad" is an obsolete unit found in some older texts and labels, contains a nonstandard metric double prefix.

Summary of obsolete or deprecated capacitance units or abbreviations: (upper/lower case variations are not shown) U+3332 ㌲ SQUARE HUARADDO is a square version of ファラッド (faraddo, the Japanese word for "farad") intended for Japanese vertical text.

The reciprocal of capacitance is called electrical elastance, the (non-standard, non-SI) unit of which is the daraf.

[17] The abfarad (abbreviated abF) is an obsolete CGS unit of capacitance, which corresponds to 109 farads (1 gigafarad, GF).

[18] The statfarad (abbreviated statF) is a rarely used CGS unit equivalent to the capacitance of a capacitor with a charge of 1 statcoulomb across a potential difference of 1 statvolt.