Congius

Ancient RomanHistorical unit (no longer in standard use)Approximate value

Six sextarii, about 3.27 L. A Roman liquid measure a little under a US gallon.

1 congius = 3.275 liters (approximately).

Approximate value. Standards for the congius varied by place and period, so this converter uses the most commonly cited value. Treat results as estimates, not exact figures.

About the congius

Eight congii made up one amphora quadrantal, and each congius was defined as a cube measuring half a Roman foot on each side. Wikipedia's table gives it as 3.27 L, which is the figure used here. The cube definition links it directly to the length standard, so any doubt about the exact length of the pes carries straight into the volume.

Inside the liquid scale, the congius was divided into 6 sextarii, and further down into 72 cyathi. Larger vessels such as the culeus were counted in congii, with 160 of them to the culeus. Because it came to roughly 3.3 L, it sits near the modern US gallon of 3.785 L, though it is noticeably smaller. Surviving vessels never match each other exactly, and the sextarii they imply range between 500 and 580 mL, so a congius from archaeology could fall anywhere from about 3.0 to 3.5 L.

Sources: Wikipedia: Ancient Roman units of measurement

Congius conversion chart

1 congius expressed in every other volume unit:

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