Pressure has a major impact on the rate of leakage from leak openings in pipes and studies have shown that the leakage exponents in networks can be substantially larger than the theoretical orifice exponent of 0.5. The most important reason for this behaviour is that leak areas are not fixed, but increase as a function of pressure. In this study, finite element analysis was used to investigate the relationship between pressure head and leak area in pipes with longitudinal, spiral and circumferential cracks. It was found that there is a linear relationship between crack area and pressure head for all crack types, pipe materials and loading conditions tested. The impact of loading, material, section and crack properties on the head-area slope was also investigated, and an attempt was made to find an expression to express the head-area slope as a function of these properties. Mathematical relationships were developed that give reasonable descriptions of the head-area slopes of longitudinal, spiral and circumferential cracks. With these relationships, it will be possible to predict the behaviour of different types of leak openings in different pipes and pipe materials.