Allometric relationships between stem variables and leaf area were determined for plantation Eucalyptus nitens (Deane et Maiden) Maiden and competing Acacia dealbata Link in 8-year-old and 4-year-old stands. Both cross-sectional area and sapwood area were considered at crown break and breast height. Whilst all four stem variables could be used to calculate tree leaf area adequately, proximity of the stem measurement to crown break was found to be more important than the choice of sapwood area or cross-sectional area in determining the closeness of the derived allometric relationship. When the relationship between sapwood area at crown break and leaf area was used, a single equation was suitable for predictive purposes across treatments for each species.