German statistician remembered for the “Engel curve,” or Engel's law, which states that the lower a family's income, the greater is the proportion of it spent on food. His conclusion was based on a budget study of 153 Belgian families and was later verified by a number of other statistical inquiries into consumer behaviour.

Engel was head of the statistical department of Saxony from 1854 to 1858, and from 1860 to 1882 he headed the Prussian statistical department in Berlin. His interest in economic statistics was generated initially by the budget studies of the French engineer Frédéric Le Play and the views of the Belgian statistician Adolphe Quételet. Among Engel's other contributions was his examination of the relationship between the size of the Prussian rye harvest and the average price of rye over a number of years prior to 1860. This was probably the first empirical study of the relationship between price and supply that underlies the theory of demand in contemporary price theory.