The objective of the paper is to develop a mathematical model to compute the chemical compositions of the organic portion of municipal solid waste (MSW) using proximate analysis data. The validation of the developed models were done using test of hypothesis and field samples. In the study, MSW samples were collected from 23 different locations throughout the year and chemical compositions of the organic matter were determined such as carbon, hydrogen, oxygen, nitrogen and sulfur using elemental analyser. Proximate analysis such as combustible volatile matter (VM) and ash content were also measured for all the sites. The range of variation in the chemical compositions and proximate analysis were observed as 5·2% ≤ carbon ≤ 21·2%, 0·64% ≤ hydrogen ≤ 2·7%, 17·2% ≤ oxygen ≤ 67·6%, 0·3% ≤ nitrogen ≤ 1·1%, 0·1% ≤ sulfur ≤ 0·37%, 9·3% ≤ VM ≤ 35·5%, 18·6% ≤ ash ≤ 72·1% on dry basis. Various statistical analyses such as standard deviation, mean, P value and F value were also carried out in the study.