The grouting has been a widely used method to strengthen weak soil in geotechnical engineering, while the issue of strength calculation for hardened grout-soil consolidation restricts the development of engineering applications. To deal with it, this study presents a quantitative strength calculation method of hardened grout-soil consolidation. On basis of the solution to the size of hardened grout, this calculation method establishes the relationship between the key grouting parameters (e.g. grouting pressure, injection rate, grout viscosity) and the strength of the hardened grout-soil consolidation. Therefore, the influence of key grouting parameters on the strength of the hardened grout-soil consolidation are obtained, and it can be concluded that higher grouting pressure, injection rate and grout viscosity tend to result in higher strength of the consolidation body. After that, a series of grouting experiments were developed to verify the suitability of the strength calculation method, and the experimental results show that the experimental values and theoretical values match to a certain extent. It is hoped that the strength calculation method could aid in the engineering applications of grouting.