The aim of this study was to develop a prediction equation for estimating the total widths of the mandibular permanent canines and premolars (TCPW) using the total widths of the mandibular first permanent molars and incisors (TWFMI). The sample comprised 288 mandibular dental casts of orthodontic patients (106 males and 182 females, average age 13.8 and 14.4 years, respectively). A digital vernier calliper was used to measure the mesiodistal tooth widths from the mandibular right to the left first permanent molar. An independent t-test was used to determine any gender difference and a multiple linear regression equation to predict TCPW using TWFMI. A paired t-test was used to compare the actual and predicted values of the canines and premolars.The results showed a statistically significant difference (P < 0.01) between the mesiodistal tooth widths of males and females. A moderate correlation and determination coefficient between TCPW and TWFMI was found (r = 0.64 to r = 0.67 and r 2 = 0.41 to r2 = 0.44, respectively). There was no significant difference between actual and predicted values for males and females. The regression equations proposed are a good prediction method to determine TCPW.