To develop an efficient and cost effective on-line method to determine the stock consistency a study on the relationship between the turbidity and transmittance of stocks and their consistency was carried out using a system consisted of a dynamic drainage jar, pump and turbidometer. Results shooed that the wavelength of 525 nm was most effective for measuring turbidity. As the consistency increases the turbidity increases, and their relationship can be depicted in the second order equations. On the other hand the relationship between consistency and transmittance can be described in exponential equations. From these equations the consistencies of stock samples can be determined using the measured values of turbidity or transmittance.