Leaf area and leaf dry biomass are key parameters linked to plant production and they are used in functional–structural plant models to simulate plant growth, but they are difficult to ascertain. Measuring leaf dimensions (length and width) to estimate them provides a non-destructive and rapid approach that can be used in the field. This was tested on teak (Tectona grandis) in Togo. Leaves were sampled to maximize variability in sizes along two categories of axes and at different ranks on the growth units. Two different equations were determined to estimate leaf area and dry biomass from leaf dimensions. The relation between leaf area (A) and the product of length (L) × width (Wi) was defined by the linear equation A = 0.60 × L × Wi whereas dry biomass (We) was predicted by a power law We = 0.004 × (L × Wi)1.11. This method could also be tested and applied to other species.