The kilogram is the base SI unit for mass (acceptable for use as weight on Earth). It uses the symbol kg.
It is the only SI base unit with the prefix as part of its name (kilo). The word is derived itself from the French 'kilogramme' which was itself built from the Greek 'χίλιοι' or 'khilioi' for 'a thousand' and the Latin 'gramma' for 'small weight'.
It is now used worldwide for weighing almost anything - and has quickly become commonly recognised and understood by the masses. It is sometimes shortened to 'kilo' which can cause confusion as the prefix is used across many other units.
In 1795 the kilogram was first used in English and was defined as the mass of one litre of water. This provided a simple definition but when used in practice it was difficult as trade and commerce often involved large items. Weighing a large object using large quantities of water was inconvenient and dangerous. As a result, an object made out of a single piece of metal was created equal to one kilogram. This platinum-iridium metal, called the International Prototype Kilogram, has been kept in Sèvres, France since 1889.
The gram is a unit of mass (acceptable for use as weight on Earth) and is a multiple of an SI base unit with the symbol g.
Although without a prefix, it actually represents 1/1000 kg. It is the first subdivision of the SI base unit; kilogram and 100 g equals 3.527396195 ounces.
It is the most common unit for measuring ingredients (except liquid) in cooking and purchasing food goods in the world today.
The majority of nutritional values and information is expressed in terms of 'per 100g'.
1 g is roughly equal to the weight of bank note or a pinch of salt.