Ounces are not all the same: avoirdupois, troy and fluid
Three different units share the name ounce. Learn which one a grams-to-ounces conversion uses and why gold and liquids need their own.
The avoirdupois ounce this tool uses
When a recipe, a parcel label or a bathroom scale mentions ounces, it means the avoirdupois ounce. It is defined as exactly 28.349523125 grams, and sixteen of them make one avoirdupois pound of 453.59237 grams. This is the ounce that a grams-to-ounces converter divides by, so every result here is an everyday weight ounce. It is the right unit for food, luggage, mail and most consumer goods.
The troy ounce for precious metals
Gold, silver and platinum are weighed in troy ounces, a survivor of a medieval system used at the market in Troyes, France. One troy ounce is about 31.1035 grams, noticeably heavier than the avoirdupois ounce. A quoted price per ounce of gold always refers to the troy ounce, so converting a gram weight of bullion with an ordinary ounce factor undercounts it by roughly ten percent. Use a dedicated precious-metal calculation instead of this tool for anything sold by the troy ounce.
Fluid ounces measure volume, not weight
A fluid ounce is a unit of volume, the space a liquid occupies, while the grams here are a unit of mass. The two only line up for water, where one US fluid ounce weighs close to 29.6 grams. For denser or lighter liquids the numbers diverge, which is why honey and cooking oil weigh differently even at the same fluid-ounce volume. Converting grams to fluid ounces requires the liquid's density, so it is a separate calculation from this weight conversion.
Weighing accurately in the kitchen
A digital kitchen scale that reads in grams gives the most reliable results because grams are small, even steps. Switch the same scale to ounces and it typically shows tenths of an ounce, which is coarser than one-gram resolution. If a recipe mixes units, convert everything to one system first, then weigh. Taring the bowl back to zero before adding each ingredient keeps running totals honest whether you work in grams or ounces.