For the design of SFRC members, the most fundamental material property is its post cracking residual tensile strength. When relying on physical models to describe structural behaviour under load, the material laws must first be accurately established. If the material laws either significantly over- or under-estimate the residual tensile capacity of the SFRC, an accurate physical model for the determination of its strength is not possible. However, in production control and materials specification, direct tensile testing is costly in time and difficult in that it requires specialised testing equipment. To this end, testing of prisms in bending is often substituted for uniaxial tension testing, and empirical design models are developed based on the results. Several attempts have been undertaken to provide an inverse analysis from prism data to establish the σ-w relationship but no direct test verification of the approaches have, to date, been established. This paper compares the results for σ-w relationship obtained from a direct tension test with those obtained using prism tests combined with an inverse analysis. Finally, a model is proposed that can be used for control testing with designs established using physically based models for strength limit states.