Abstract: Leaf area is an important indicator in evaluating plant growth, which is often measured by the so-called length-width method in practice. With this method, tobacco leaves' length and width were measured and the leaf area was calculated by multiplication of the empirical correction coefficient 0.6345. However, it is rarely reported in the literature whether the coefficient is suitable in measuring tobacco leaf area at the seedling stage. 246 tobacco leaves were collected at the seedling stage and leaf areas were measured by three methods namely scanning calculation method, photocopy weighing method and length-width method. The results showed: (1) Using the empirical correction coefficient reported in the literature, leaf area measured by the length-width method was significantly lower than that measured by the scanning calculation method and the photocopy weighing method. (2) No significant difference was observed between the length-width method revised coefficients obtained through the scanning calculation method and the photocopy weighing method on different sizes of leaves at tobacco seedling stages. (3) The relative errors were less than 1% and 2% respectively by comparisons of leave areas measured by the scanning calculation method and the photocopy weighing method with those measured by the length-width method using the revised correction coefficient. The correlation coefficients were 0.9963 and 0.9966, respectively. Accordingly, we believe that the correction coefficient of the length-width method should be revised as 0.7075 to calculate tobacco leaf areas accurately at the seedling stage.