Conversion from 4 US Dry pints to Gallons

Information about the US Dry pint (pt)

The United States dry pint is a unit of volume equal to 550.610471 millilitres, or 33.6 cubic inches. Its symbol is pt. It belongs to a separate American measuring system used for produce and grain rather than for liquids, and it is about sixteen per cent larger than the United States liquid pint of 473 millilitres.

Two parallel chains exist because two kinds of goods were once measured differently. Liquids descend from the wine gallon of 231 cubic inches, while dry goods descend from the Winchester bushel of 2150.42 cubic inches, a corn measure standardised in medieval England. Dividing the bushel by four gives a peck, by thirty-two a dry quart, and by sixty-four a dry pint, and none of those figures has any relation to the liquid chain.

Berries are where the unit is still met. Blueberries, raspberries and strawberries are sold in American markets in pint and quart baskets, and the basket is a dry measure. A pint of blueberries is therefore 551 millilitres of fruit, not 473, and a shopper comparing that basket with a pint of cream is comparing two different quantities under one name.

Nothing on a label resolves the ambiguity. Both are written pt, both are called a pint, and the word gives no clue as to which chain is meant. In practice the contents decide: if it pours, it is liquid measure, and if it is heaped, it is dry. That rule is reliable but it is nowhere written down, which is why converted American recipes so often disagree with one another.

Its existence is a survival from selling by bulk. Before cheap accurate scales, grain, apples, potatoes and shellfish were sold by filling a stamped measure and levelling it off, and the whole dry chain from bushel down to pint served that trade. Almost all of it has now been replaced by weight, and United States produce regulations increasingly specify pounds instead.

For conversion, the safest approach is to abandon the name entirely. A dry pint is 551 millilitres, a dry quart 1101, a peck 8.81 litres and a bushel 35.24. Writing the metric figure removes an ambiguity that the English word carries and cannot shed.

One United States dry pint equals 550.61 millilitres, 33.6 cubic inches, half a US dry quart, or about 1.164 US liquid pints.

Information about the Gallon (gal)

The gallon in the imperial system is a unit of volume equal to exactly 4.54609 litres. Its symbol is gal. It contains four quarts, eight pints and 160 imperial fluid ounces, and it is about a fifth larger than the United States gallon, a difference that causes more confusion than any other single discrepancy between the two systems.

Its original definition was elegant. The Weights and Measures Act of 1824 fixed the imperial gallon as the volume occupied by ten pounds of distilled water at sixty-two degrees Fahrenheit under a barometric pressure of thirty inches of mercury. That tied liquid measure directly to the avoirdupois pound, so a gallon of water weighed ten pounds and a pint weighed a pound and a quarter. In 1985 the definition was replaced by the exact metric figure, but the old relationship still holds to within a fraction of a per cent.

Fuel economy keeps it in daily use. British and Irish drivers describe consumption in miles per gallon even though fuel has been sold in litres since the 1990s, and the figure is an imperial one. The same car scores about twenty per cent higher in British miles per gallon than in American, purely because the gallon is larger, which is why cross-Atlantic comparisons of efficiency are meaningless unless the gallon is specified.

Legal use in Britain is now narrow but real. Draught beer and cider must be sold in pints, half pints or third pints, and milk in returnable containers may be sold in pints, which keeps the whole imperial chain alive by keeping its smallest working member alive. Several Caribbean territories still sell motor fuel by the imperial gallon.

The difference from the American gallon is worth stating plainly. One imperial gallon is 4.546 litres and one United States gallon is 3.785, so an imperial gallon is 1.2 United States gallons. Recipes, fuel figures, tank capacities and chemical dilutions all break if the wrong one is assumed, and the error is large enough to matter but small enough to look plausible.

Below it the chain runs quart, pint, gill and fluid ounce, each a quarter or a fifth of the one above rather than a decimal step. That structure was designed for dividing a container by halving it repeatedly, which is a practical merit when pouring and a serious nuisance when calculating.

One imperial gallon equals 4.54609 litres, 8 imperial pints, 160 imperial fluid ounces, or about 1.201 US gallons.