From the beginning, the assessment of membership function in fuzzy mathematics is a demanding task. The extraction of the membership function is ambience dependent and thus complication exists in the process of evaluation. In this assessment, the main work deals with the derivation of fuzzy membership function where numerical data is available. The numerical interpolation and defuzzification technique are used here. Many types of fuzzy number have been used to find out the membership function. In this paper, we mainly used triangular fuzzy number to construct the membership function. A case study is furnished to emphasise the advantage of adopting the method.