amperage (n.)

1881, "the current that one volt can send through a resistance of one ohm," from French ampère, named for French physicist André-Marie Ampère (1775-1836). Adopted by the Electric Congress at Paris in 1881. Shortened form amp is attested from 1886.

"electromotive force reckoned in volts," 1882, from volt + -age.

word-forming element in nouns of act, process, function, condition, from Old French and French -age, from Late Latin -aticum "belonging to, related to," originally neuter adjectival suffix, from PIE *-at- (source of Latin -atus, past participle suffix of verbs of the first conjugation) + *-(i)ko-, secondary suffix forming adjectives (see -ic).