The aim of the study was to analyze the extent of involvement of labour in manual chopping of paddy straw and also to determine its optimum size for the development of paddy straw collector-cum-chopper to degrade the valuable agro residue in shortest possible time for value added product using microbial inoculants for composting. Three sizes were selected; after harvest, single blade chopping (CPS4-5 cm) and two blades chopping (CPS2-3 cm) of manually operated chaff cutter. Three different doses of compost inoculant prepared from Aspergillus awamori, Trichoderma viride and Aspergillus nidulans (T1: untreated; T2: 300 g; T3:500 g; T4: 1000 g) were applied on the paddy straw for conversion to compost. The moisture content was maintained at 60 % of water holding capacity (WHC) by adding water at different intervals.  The straw size of CPS4-5 cm with T8 treatment surpasses all other treatments in terms of low cost for chopping and power consumption along with improvement of selected parameters – pH 7.0 with subsequent increase in electrical conductivity 0.5 dS/m, nitrogen content 0.78 %, phosphorus 93.7 ppm, potassium 0.69 % with 56.9 % decrease in carbon content from first turning to fourth turning in 35 days. The C: N ratio decreased from 84.89 to 18.70 (a reduction of 77.97 %) from initial value and is a definite parameter for conversion of substrate to compost. The study showed that though some of the parameters for CPS2-3 cm were better than that of CPS4-5 cm at 1000 g inoculant dose (T₈ and T₁₂), overall the latter was found to be the best size for the development of paddy straw collector-cum-chopper as well as preparation of compost in shortest possible time.