The content of fatty acid methyl esters (FAME) is a crucial property of biodiesel and serves as an indicator of the transesterification reaction that converts vegetable oil into biodiesel. To facilitate the rapid estimation of FAME quickly in the biodiesel industries, simple methods such as measuring refractive index, density, and dynamic viscosity measurements were employed to monitor the progress of transesterification of castor oil to biodiesel. Blends of castor oil and biodiesel were mixed at different weights to find correlations between FAME content and refractive index, density, and dynamic viscosity measurements. The transesterification of castor oil with methanol was carried out to examine how the refractive index, density, and dynamic viscosity properties change in relation to the conversion ratio. The results show that the optimal conditions for the transesterification of castor oil with methanol involve using a
methanolic solution of KOH at 45 °C and 150 min with 18:1 mole ratio. This study demonstrated that these measurements were simple, fast, and suitable for monitoring the conversion of castor oil to its methyl and determining the % FAME content in  castor biodiesel prepared.