To provide an estimation method in which a parameter in a large tank can be estimated and predicted with sufficient accuracy, by a method wherein a suspension as a sample is placed stationarily for a set time in a small container so as to be fractionated into an upper layer and a lower layer, and an average particle sinking speed is computed.

An average particle sinking speed Vav of solid particles in a suspension inside a container is found by means of Vav=(C-Ca)H(1-Ca)Ct, where C represents the computed initial particle size concentration of the suspension, Ca represents a particle concentration in an upper layer, H represents the height of the upper layer, and (t) represents the stationary time. A deposition speed Vp of a deposit having an assumable arbitrary concentration is found by means of Vp=Vav×(1-C) Cρ/(Cf-C)ρf, where Cf represents an assumed particle density of a deposit, ρ represents an initial density of the suspension and ρf represents an assumed density of the deposit. When an average sinking speed is found regarding a suspension which is filled into a small container such as a beaker or the like, a deposition speed which is generated in a suspension which is filled into a large tank can be found on the basis of its value, various parameters can be estimated.