In the present work analytical formulas for the effective volumes and effective surfaces for bimodular rectangular bars loaded in flexure have been provided. As well, strength scaling ratios from one flexural loading configuration to another with various Weibull modulus have been made available. Generally, strength scaling for specimen size is dependent on whether the flaws are volume or surface distributed, however in this study it has been observed that the ratio of strengths from any two configurations, such as three-point flexural to four-point, is independent of whether the flaws are volume or surface distributed when the cross sectional sizes are the same.