The plastic woven sack industry in Thailand is growing and competitive. A study found that the current production cost calculation method used by manufacturers does not accurately reflect the actual costs. By analyzing the production structure and costs, the study developed a new method that estimates production costs more precisely. The new method considers material loss in production, separates direct labor costs from overhead costs, and includes all overhead costs in the calculation. The study showed that the traditional method overestimates unit production costs by around 10%, with direct material costs higher by 7% and direct labor costs overestimated by 27%.