The purpose of this study was to derive new mathematic formulae that could be used reliably to predict water permeability of surgical fabrics before they are made and tested for water Permeability. Such a theoretical prediction of water permeability, Qprd, of surgical fabrics is needed for not only timely characterization but also for assisting in more efficient future design and development of better surgical fabrics. Two mathematic formulae, Q, and Qk, were derived from the Buckingham Pi Theorem, in which relevant fiber and fabric parameters were placed into dimensionless T groups and computed for 25 commercial and experimental vascular fabrics. Linear regression analysis of the relationship between these T groups with water permeability on the woven and knitted grafts yielded coefficients for the corresponding T groups that were required for constructing appropriate mathematic formulae to predict water permeability of vascular fabrics. When proper sources of the experimentally determined water permeability, Qexp, were chosen for comparison, we found that 86% of woven fabrics (6 of 7 ) and 77% of knitted fabrics (14 of 18) had their Qprd within 10% of their Qexp. This high percentage of close matching (within 10%) between Q and Qexp should be considered satisfactory because tg: experimental error for obtaining Qexp is generally higher than 10%. The difference between Qprd and Qexp ranged from as small as 0.27% to as high as 74.2%, depending on the type of fabrics and source of Qexp. It appeared that the formulae worked well with fabrics of simpler structure such as those experimental woven vascular fabrics that showed 100% close match between Qprd and Qexp: Nonlinear relationship among the parameters and additional new parameters are required to fine-tune for existing mathematic formulae to improve their accuracy of predicting water permeability for more complex fabric structures such as knitted fabrics. A computer program had been written that uses these theoretical formulae for predicting water permeability of vascular fabrics. Users could simply input five major fabric and fiber parameters of a surgical fabric and the computer would calculate its water permeability instantaneously.