Difference between Imperial Gallon and Congius

IMPERIAL GALLON vs CONGIUS: NOUN

A unit of measure for liquids used in the British Isles and in some Commonwealth countries, equivalent to 8 imperial pints, 4.55 litres, or 1.20 U. S. gallons.
A British imperial capacity measure (liquid or dry) equal to 4 quarts or 4.545 liters

An ancient Roman liquid measure, being six sextarii or one eighth of an amphora; also used as a weight measure during the reign of Vespasian, being the weight of that volume of water.
A gallon, or four quarts.
A liquid measure containing about three quarts.
In pharmacy, a gallon.
A measure of capacity among the ancient Romans, the eighth part of the amphora.
An ancient Roman measure for liquids, equal to about seven eighths of a US gallon (3.3 liters).
A gallon.
A British imperial capacity measure (liquid or dry) equal to 4 quarts or 4.545 liters

Quart, Metric capacity unit, Litre, Dry measure, Muchkin, Millistere, Liter, Metric unit, British capacity unit, Liquid unit, Mutchkin, Vedro, Liquid measure, Congius, Gallon

Vase, Pocket flask, Dolium, Inurn, Holmos, Sextary, Potstone, Situla, Urn, Tea urn, Dice cup, Amphora, Congiary, Imperial gallon, Gallon

Quart, Metric capacity unit, Litre, Dry measure, Muchkin, Millistere, Liter, Metric unit, British capacity unit, Liquid unit, Mutchkin, Vedro, Liquid measure, Congius, Gallon

Vase, Pocket flask, Dolium, Inurn, Holmos, Sextary, Potstone, Situla, Urn, Tea urn, Dice cup, Amphora, Congiary, Imperial gallon, Gallon

The Imperial gallon was originally defined as convert of water in 1824, and refined as exactly 4.54609 litres in 1985.
By special exception, BRNIR is available in its original Imperial gallon containers.