The span range of precast prestressed concrete girders (PPCGs) is increasing owing to the advances and improvements in concrete and both transport and lifting technologies. One risk of stretching PPCGs while keeping the same cross section geometry and/or maximizing the prestress force is the increase of lateral instability failures during transient load situations (e.g., transport, lifting and temporary support conditions). Even though most girders are designed according to the regulations gathered in current codes, the occurrence of such failures emphasize the need of new approaches to deal with this problem with higher reliability. In view of this, the main objective of this study is to propose a new formula derived from a physical model meant for checking the cracking risk of PPCGs hanging from cables. This formula allows estimating the cracking safety factor including the most relevant geometric and mechanical variables that govern the problem. Some of the paramount variables (such as precamber, lateral sweep and compressive concrete strength) can be measured before the lifting operations and, thus, maximize the reliability of the approximation. An example of application of a real case is also included and several conclusions are finally drawn resorting to a Monte Carlo analysis.