Concrete cracking is a challenging and uncertain design criterion that significantly affects our ability to predict the serviceability of reinforced concrete (RC) structures. It is evident that the concrete cracking strength depends on the test method, such as flexural strength, splitting tensile strength and direct tension. Moreover, prediction models proposed by design codes have wide variation. The uncertainty of the cracking strength determined experimentally or numerically reduces confidence in serviceability limit state design when compared with strength limit state design. However, this uncertainty cannot be claimed as a random uncertainty but rather as an epistemic uncertainty. Intervals can be used to describe this uncertainty using possibility theory, a mathematical framework to represent a kind of epistemic uncertainty known as non-specificity. A methodology is introduced here to establish a concrete cracking strength interval. A case study to use this cracking strength interval to predict an RC deflection interval is presented.