To investigate the effects of bond sizes (including width and thickness) on the idealized inter-granular mechanical properties of cement, an unified strength expression of cement is proposed with considering the bond sizes, based on the previous research results and the results of experiments performed on inter-granular bonds with different sizes. The results reveal that, both the peak compression force and tension force are associated with the factor λ which is representable for the end constraint and the factor ξ which refers to the ratio of height to width of samples. Shear and torsional capacity of cemented sample with different bond sizes can be expressed uniformly by the fitted shear coefficient and anti-rotation coefficient. In the three-dimensional peak force space, the strength envelopes of the cemented samples of different bond sizes show opening hollow oval balls. In addition, the values of the peak forces increase significantly as the bond width increases; the values of the peak forces decrease with the increase of bond thickness,and when the bond thickness approaches a certain extent, the trend of force decrease becomes insignificant.