Conversion from 5 Milligrams to Hundredweights

Information about the Milligram (mg)

The milligram is a unit of mass equal to one thousandth of a gram, or one millionth of a kilogram. Its symbol is mg. It is the smallest mass most people encounter by name, and the one printed on nearly every medicine box and nutrition label.

Pharmacy is built on it. Tablet strengths are quoted in milligrams almost universally, from a 500 mg paracetamol tablet to a 5 mg dose of a cardiac drug, and dosing by body weight is written in milligrams per kilogram. The unit suits the job because the therapeutic range of most oral drugs falls between one and a thousand milligrams, so doses can be stated as whole numbers without prefixes or decimals.

Nutrition labels use it for the minerals and for anything present in quantities too small for grams. Sodium, calcium, potassium, magnesium, iron and vitamin C are all listed in milligrams, and so is cholesterol. Caffeine content is given the same way: a strong cup of coffee holds roughly 100 mg, and regulators in several countries require energy drinks above 150 mg per litre to carry a warning.

In the laboratory the milligram is the comfortable working range of an analytical balance, which typically reads to a tenth of a milligram and settles within seconds. Below that, weighing becomes an exercise in controlling draughts, static electricity and the operator’s own body heat, which is why sub-milligram quantities are usually prepared by dissolving a larger weighed mass and taking an aliquot rather than by weighing directly.

Law and public health borrow it whenever a limit has to be enforceable. Drink-driving is defined in most of Europe as 50 milligrams of alcohol per 100 millilitres of blood, and in the United Kingdom as 80; food regulations cap sodium, additives and contaminants in milligrams per kilogram; and vehicle emission standards are written in milligrams per kilometre for particulates and oxides of nitrogen. In each case the number has to be small enough to matter biologically and large enough to be measured reliably in an ordinary testing laboratory, and the milligram sits at exactly that point. A cup of coffee carries about 100 milligrams of caffeine, which is a useful mental anchor for the whole scale.

One milligram equals 0.001 grams, one thousand micrograms, and one millionth of a kilogram.

Information about the Hundredweight (cwt)

The hundredweight is a unit of mass whose value depends on which side of the Atlantic you are standing. The imperial or long hundredweight is 112 pounds, about 50.802 kilograms. The US or short hundredweight is 100 pounds, about 45.359 kilograms. Its symbol is cwt, from the Latin centum and the English weight.

The name promises a hundred and the imperial version delivers a hundred and twelve, which looks like an error until the arithmetic behind it is seen. Twenty hundredweight make a long ton of 2240 pounds, and a hundredweight is eight stone of fourteen pounds each. The chain of halvings and doublings that runs from the pound to the ton only closes neatly if the intermediate unit is 112, so the number is a consequence of the system rather than a mistake in it.

Its working life was in bulk trade. Coal, cement, grain, potatoes and fertiliser moved by the hundredweight, and sack sizes were built around it: the standard British coal sack held one hundredweight, which is why a coal merchant's cart was rated in a number of hundredweight rather than in tons. Vans and light trucks were once classified the same way, and the phrase survives in some vehicle names.

In the United States the short hundredweight is still used in agricultural markets, where livestock, grain and milk prices are quoted per hundredweight rather than per pound or per ton. Elsewhere the unit has largely given way to the tonne and the kilogram, and its main modern role is to make old records intelligible.

Continental Europe kept a cousin of it under a different name. The quintal, from the Arabic qintar by way of medieval Latin, served the same purpose in French, Spanish, Italian and Portuguese trade, and when the metric system arrived it was simply redefined as a round 100 kilograms. That metric quintal is still the unit in which grain harvests are reported across much of southern Europe, Latin America and India, and it sits close enough to the imperial hundredweight of 50.8 kilograms that old and new figures can look deceptively similar. The parallel is instructive: both units survived because a sack a strong worker could handle is a more natural quantity than any round metric mass.

One imperial hundredweight equals 112 pounds, about 50.802 kilograms, or 8 stone.