Abstract: The number conversion algorithm from positional notation with one radix into positional notation with bigger radix has been presented in this study. The algorithm correctness has been proved. Suggested algorithm is the most efficient among known ones because the conversion is carried out in m-1 steps where m is the number of digits. The number of steps can vary from m-1 up to m (m-1)/2, and calculation at each step is limited to multiplication of two one-digit numbers and subtraction (addition) of the product from the result received at the previous step (in case of a variant of algorithm with number of steps m (m-1)/2 ).