Jet grouting is proven to be a reliable and effective technique for ground improvement. The method has been successfully used for a wide range of application in foundation engineering such as underpinning, retaining wall constructions and cut off walls. The basic principle is to use a high pressure jet of water-cement-slurry to destroy the soil structure. The slurry is mixed with the grains of the soil and becomes hard. An essential disadvantage of the method is given by the determination of the range of the jet, which is still not feasible with sufficient reliability or only with considerable technical and economical effort. The research work is related to this problem. In a first step a mathematical model is developed which correlates on the basis of a mass-balance formulation the components of the inflow during the jet grouting process, the eroded masses of the soil and the waste slurry. The proposed model allows a more realistic calculation of the diameter of jet grouted columns. So the efficiency of the jet grouting method can be increased in terms of economy and reliability.