Congius, congij, m. g. Mensuræ liquidorum genus est, x sextarios concinens. Plin. A measure, after Budey, the eyght part of Amphora, conteyning stxe Sextarios. Enery Sextarius beyng 24 ounces, that is, a wine piute and a halfe. So that Congius is of our measure a gallon and a pint. If you take Sextarins for 18. ounces as phisttions do: or for twentie ounces as Agricola doth, then is it but a potteil, a quarte, halfe a pinte and 4. ounces, or otherwise according to the rate. It is vsed for our gellon.
Lewis and Short: Latin dictionary
congĭus, ii, m., a Roman measure for liquids, containing the eighth part of an amphora, six sextarii, or twelve heminae; = about 206 cubic inches or nearly six pints English, Cato, R. R. 57; Liv. 25, 2, 8; Plin. 14, 9, 11, 85; 14, 22, 28, 144 and 146 al.; cf. Fest. p. 246, 4 Müll.; Isid. Orig. 16, 26, 6 sq.; Rein in Becker, Gallus, 3, p. 219 sq., and Dict. of Antiq. s. v.