Definition of Ingredient Density
Ingredient density describes how much mass fits into a certain volume of an ingredient. In cooking, it explains why the same cup size can give different weights for flour, sugar, oats, cocoa, or butter.
This is the key reason grams-to-cups and cups-to-grams conversions change by ingredient. A cup of flour is lighter than a cup of honey or butter because the ingredients do not fill space in the same way.
Ingredient density can also shift slightly with measuring method. Sifting, packing, chopping, and moisture level can all change how much an ingredient weighs in a cup or spoon.