The ounce is a unit of mass (acceptable for use as weight on Earth) and is part of the imperial system of units. It has the symbol oz.
Not to be confused with a fluid ounce (fl oz; volume) or an ounce-force (force), the ounce is the smallest of the 3 denominations of weight used in the imperial system. There are 16 ounces in a pound and 14 pounds in a stone.
The strict name for this unit is the avoirdupois ounce and in SI / metric terms it is equivalent to approximately 28.3g.
Ounces are used to indicate the weight of fabrics in Asia, the UK and North America. For example, 16 oz denim. The number refers to weight of the fabric in ounces.
The ounce was no longer seen as a legal unit of measure after the year 2000 in the UK. However, it is still used informally and is also used as the measure for portion sizes in restaurants in the UK.
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.