ABSTRACTLeaf development is affected by both internal (genetic) and external (environmental) regulatory factors. The aim of this work was to investigate how leaf growth variables are related to one another in a range of environments. The leaf growth variables of wild‐type Arabidopsis thaliana and leaf development mutants (ang4, ron2‐1, elo1, elo2 and elo4) were studied under different incident light treatments (light and shade). The leaves studied were altered in various leaf development variables, such as the duration of expansion, relative and absolute expansion rates, epidermal cell size, epidermal cell number and initiation rate. Final leaf area was correlated to maximal absolute leaf expansion rate and cell number, but not to duration of leaf expansion or cell size. These relationships were common to all studied genotypes and light conditions, suggesting that leaf size is determined early in development. In addition, the early variables involved in leaf development were correlated to one another, and initial relative expansion rate was negatively correlated to the duration of expansion. These relationships between the leaf development variables were used to construct a conceptual model of leaf size control.