Greek κοδράντης. Literally "a quarter". Also called Kodrantes.
A quarter of an assarion — the coin Mark reaches for when he has to explain how little two lepta were.
Wage
about 11 minutes' work (about 11 minutes' work).
Reckoned from a quarter of an assarion.
Diameter
1.6–1.9 cm (0.63–0.748 in).
Reckoned from surviving quadrantes of Augustus and Tiberius.
The quadrans is a quarter of an assarion, and it exists in the New Testament mostly as a unit of explanation. Mark, writing for a Roman readership, tells them the widow's two small coins came to one quadrans — because "two lepta" would have meant nothing to them and "a quadrans" meant the smallest Roman coin there was. Older English versions render it "farthing", which they also use for the assarion.
Sizes are the range of surviving examples, and coins of one name varied from mint to mint. Bronze paid for small things and silver for wages and taxes: the widow gave two lepta (Mark 12:42), the temple tax was a didrachma (Matthew 17:24), and a stater paid it for two (17:27).