Accurate and effective performance estimation of thermoelectric generators with optimized structure is essential for large-scale energy harvesting applications. This paper aims to study and analyze a bismuth telluride-based thermoelectric generator using finite element analysis. The impact of thermoelements length and area on obtaining an optimal temperature gradient, output voltage generation, and maximum output power is investigated. The proposed thermoelectric generator module, which is consisted of eight pairs of p-type and n-type bismuth telluride thermoelements, produced an optimum temperature gradient and output voltage of 96.6 mV with each thermoelement length of 8 mm and area of 1 mm2. In addition, the effect of varying thermoelements area with optimal length on thermoelectric generator performances is also presented. These outcomes could be utilized to fabricate a bismuth telluride-based thermoelectric generator with optimized thermoelements.