Many vision-based techniques have been proposed and handheld devices have been commercially available for leaf area measurement. However, they are not cost-effective nor simple enough for use. As an effort to tackle this problem, this study proposed an easy vision-based approach toward measuring the leaf dimensions and area using a smartphone, a cost-effective and available device. Acceptable measurement accuracies were achieved from experiments with different leaf shapes and sizes in terms of both error and error percentage. The leaf area had the largest error percentage of 2.3%; however, its largest mean error percentage was only 0.6 ± 0.5%. The smallest error was associated with the leaf width with the largest mean error and mear error percentage of 0.61 ± 0.35 mm and 1.5 ± 1.0%, respectively. It is thus promising to apply this simple approach for screening the dimensions and area of many leaves with different shapes and sizes.