From BiblePortal Wikipedia

Hastings' Dictionary of the New Testament [1]

Firkin ( μετρητής,  John 2:6 only).—An Attic liquid measure, which is generally regarded as the equivalent of the Hebrew bath (cf. LXX Septuagint  2 Chronicles 4:5), and is therefore ‘able to contain seventy-two sextaries’ (Josephus Ant. viii. ii. 9), accurately 71, 28 pints, or approximately 9 English gallons. ‘Firkin’ (Authorized Version and Revised Version NT 1881, OT 1885)—the fourth part of a barrel containing from 32 to 36 gallons—as a translation is sufficiently exact for ordinary purposes.

Previously emptied for the ablutions of the guests, the water-pots are filled afresh. Their character and contents prove the reality of the miracle. Very effective is the touch added by the expression ἕως ἄνω, ‘up to the brim,’ if only in presenting a sure basis for calculating the quantity of this wedding gift. The lowest estimate of the quantity of wine must be over 12 firkins or 108 gallons; yet, had the vessels been larger they had been filled; had there been more vessels, more wine. To such lavishness there need not be imputed indiscretion. Our Lord did not give simply to meet a pressing need, or even for future use, but rather to exemplify the illimitable power of the Giver. ‘It is His first miraculous sign … it must become the type of the fulness of grace and joy and strength which the only-begotten Son brings to the earth’ (Godet on  John 2:6).

Literature.—Art. ‘Weights and Measures’ in Hasting's Dictionary of the Bible, iv. 911–913; Encyc. Bibl. iv. col. 5294 f.

Alex. A. Duncan.

Vine's Expository Dictionary of NT Words [2]

1: Μετρητής (Strong'S #3355 — Noun Masculine — metretes — met-ray-tace' )

is a liquid measure (akin to metreo, "to measure"), equivalent to one and a half Roman amphoroe, or about nine gallons,  John 2:6 .

American Tract Society Bible Dictionary [3]

 John 2:6 , a Greek measure, equivalent to the Hebrew bath, and containing seven and a half gallons. The quantity of wine produced by the miracle at Cana was large: but the assemblage was also large; the festivities continued, it may be, a whole week,  Judges 14:12; and many would be drawn to the scene by hearing of the miracle.

Webster's Dictionary [4]

(1): ( n.) A varying measure of capacity, usually being the fourth part of a barrel; specifically, a measure equal to nine imperial gallons.

(2): ( n.) A small wooden vessel or cask of indeterminate size, - used for butter, lard, etc.

Smith's Bible Dictionary [5]

Firkin. See Weights and Measures .

Holman Bible Dictionary [6]

 John 2:6Weights And Measures

Hastings' Dictionary of the Bible [7]

FIRKIN . See Weights and Measures.

Easton's Bible Dictionary [8]

 John 2:6

Morrish Bible Dictionary [9]

See Weights And Measures

International Standard Bible Encyclopedia [10]

fûr´kin ( μετρητής , metrētḗs ): The liquid measure used in  John 2:6 to indicate the capacity of the water-pots mentioned in the narrative of the miracle of turning the water into wine. It is regarded as equivalent to the Hebrew bath , and thus contained about nine gallons. See Weights And Measures .

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [11]

( Μετρητής , a measurer, occurs only in  John 2:6), a metretes, i.e. the Attic Amphora a -measure for liquids, equivalent to thee Hebrew BATH, and containing about 8S gallons (Smith's Diet. Of Class. Antiq. S. v. Metretes). (See Metrology).