A method of determining shear strength of soil using a fall cone apparatus is provided. The method includes generating a first plot having graph lines defined for penetration depth values ranging from 4 to 20 mm on a first logarithmic paper, deducing a first mathematical model based on the first plot, and generating a second plot having the graph lines extended for a predefined penetration depth range based on the first mathematical model. The method further includes generating a third plot having graph lines corresponding to the extended penetration depth values defined for the W/A ratio values ranging from 0.17 to 13.3 on a second logarithmic paper, deducing a second mathematical model based on the third plot, generating a fourth plot having the graph lines extended for a predefined W/A ratio range based on the second mathematical model, and determining shear strength based on the fourth plot.