Pile foundations, either precast or cast-in-situ, are popular for usage worldwide in many important and costly projects such as bridges in transportation networks, or jetties in harbor areas, etc. In addition, the stability and safety of such strategic structures count to a great extent on the serviceability of the piled foundations. Thus it is very important, from the structural analysis point of view, to achieve an accurate approach to calculate the pile group stiffness with respect to the lateral loads. Calculating the pile group stiffness in free air will be very easy but the puzzle remains the calculating of pile group stiffness in the soil because the soil provides confinement zone around pile group, such this confinement causes increasing the stiffness of pile group. Many factors may affect the pile group stiffness such as pile diameter, pile length, spacing, soil type, etc. During last decision the investigators tries to achieve a general formula for calculating pile group stiffness. Different methods and approaches for determining the pile group stiffness were presented. Each approach or method has its own assumptions, validation band, advantages and disadvantages which limit the usage validity. This paper presents a study on three methods commonly used to plot the p-y curve which in turn used to calculate the pile group stiffness with respect to lateral loads. Throughout this study, the studied methods were applied on a specified case study. A comparison was made between the outputs of the different calculation methods and field measurements of pile lateral displacement. Subsequently, recommendations for the validity of each approach are stated.