A theoretical formula based on a newly established knit unit model of three dimensional structure has been derived in order to predict the stitch length of a sinker pile warp knit fabric. In this formula. stitch length of the fabric is expressed as the functions of wale and course spacing, yarn diameter and pile height which are usually used in the knitting mills for production and quality control. And the possibility of the modification of the existing formulas, proposed for ordinary warp knit fabrics was also discussed. Comparison of the existing theoretical values with the experimental ones revealed that the most satisfactory results were obtained from the new modified derived theoretical formula.