abfarad

The abfarad is a unit of electrical capacitance derived from the centimeter-gram-second (CGS) system of measurement. One abfarad equals 109 farads, or one gigafarad in modern SI terminology. It was used primarily in electrical engineering during the early-to-mid twentieth century, before the SI system became the global standard for scientific and industrial measurement.

The unit emerged from the electromagnetic CGS system, which defined electrical quantities in terms of mechanical and magnetic relationships rather than as independent fundamental dimensions. In this framework, capacitance was expressed through the electromagnetic unit (emu) system, where the abfarad represented the capacitance of a conductor whose potential rises by one abvolt when charged by one abcoulomb. This inheritance of the ab prefix, meaning tenth of a unit in the CGS-emu system, explains the term itself.

Because 109 farads is an impractically large capacitance for real circuits, the abfarad was rarely encountered in actual component specifications or laboratory work. Practical capacitors used microfarads (µF), nanofarads (nF), or picofarads (pF). The unit was more common in theoretical texts and in publications from Eastern European and Soviet technical traditions, which retained CGS conventions longer than Western industry.

The replacement of CGS by the International System of Units (SI) during the 1960s and 1970s eliminated the need for the abfarad. Today it appears only in historical technical documents and older reference materials. Engineers and technicians working with legacy equipment or archived schematics may encounter the term, but conversion to farads is straightforward: divide abfarads by 109 to obtain farads, or multiply by 1000 to obtain picofarads.