Quality function deployment (QFD) is a planning and problem-solving methodology that is widely used for translating customer requirements (CRs) into engineering characteristics (ECs) of a product. Estimating the correlation measures among ECs for product planning house of quality (PPHOQ) is a crucial step of the QFD implementation process. This study presented a rough set based methodology for estimating the correlation measures by discovering the knowledge and experience of QFD team, with the help of introducing a concept of the category factor of a correlation. A case study of two-cylinder washing machine is used to demonstrate the proposed methodology.