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Dry measures are units of volume used to measure bulk commodities which are not gas or liquid. They are typically used in agriculture, agronomy, and commodity markets to measure grain, dried beans, and dried and fresh fruit (e.g. a peck of apples is a retail unit); formerly also salt pork and fish. They are also used in fishing for clams, crabs, etc. and formerly for many other substances (e.g. coal, cement, lime) which were typically shipped and delivered in a standardized container such as a barrel.
In the original metric system, the unit of dry volume was the stere, but this is not part of the modern metric system; the liter and the cubic meter are now used. However, the stere is still widely used for firewood.
Imperial and U.S. customary units
In U.S. customary units, most units of volume exist both in a dry and a liquid version, with the same name, but different values: the dry hogshead, dry barrel, dry gallon, dry quart, dry pint, etc. The bushel and the peck are only used for dry goods. Imperial units of volume are the same for both dry and liquid goods. They have a different value from both the dry and liquid US versions.
Many of the units are associated with particular goods, so for instance the dry hogshead has been used for sugar and for tobacco and the peck for apples. There are also special measures for special goods, such as the cord of wood, the sack, the bale of cotton, the box of fruit, etc.
Because it is difficult to measure actual volume and easy to measure mass, many of these units are now also defined as units of mass, specific to each commodity, so a bushel of apples is a different weight from a bushel of wheat (weighed at a specific moisture level). Indeed, the bushel, the best-known unit of dry measure because it is the quoted unit in commodity markets, is in fact a unit of mass in those contexts.
US dry measures are 16% larger than liquid measures; this is advantageous when cooking with fresh produce, as a dry pint of vegetables after trimming ends up being about a cooking (liquid) pint.
Struck and heaped measurement
The volume of bulk goods is usually measured by filling a standard container, so the containers' names and the units' names are often the same, and indeed both are called "measures". Normally, a level or struck measure is assumed, with the excess being swept off level ("struck") with the measure's brim—the stick used for this is called a "strickle". Sometimes heaped or heaping measures are used, with the commodity heaped in a cone above the measure.
As far back as medieval times, if not Biblical times, there was pressure from landowners to demand heaped bushels of commodities from their peasants, while at the same time peasants were obliged to purchase commodities from stricken containers. Rules outlawing this practice were circumvented through use of heavy round strickles, which would compress the contents of a bushel.
U.S. units of dry measure
- 1 pint (pt) = 0.550610471 L
- 1 quart (qt) = 2 pt = 1.101220942715 L
- 1 gallon (gal) = 4 qt = 268.8025 in³ = 4.40488377086 L
- 1 peck (pk) = 8 qt = 2 gal = 8.80976754 L
- 1 bushel (bu) = 2150.42 cu in = 4 pk ≈ 35.2391 L
- Kula, Witold (1986). Measures and Men Princeton: Princeton Univ. Press.