Although natural ventilation has low efficiency and stability, its simulation remains relevant today. First, most of the legacy buildings are naturally ventilated. Secondly, production facilities with powerful heat emissions are designed precisely with the use of natural ventilation – aeration. After all, the air exchange in them is too great to provide it with mechanical systems. Finally, it is impractical to utilize the heat of the exhaust air due to the lack of close consumers of low-grade heat. Previously, when calculating aeration, only the value of the coefficient of the flow rate of holes in the self-similar area was used for the calculated parameters of the indoor and outdoor air. Modern approaches require modeling air exchange under variable internal and external conditions, under which air exchange can take arbitrarily small values. In this case, the mode of operation of the holes goes beyond the self-similar area. The most versatile is the Altshul chart. The diagram was built before the advent of powerful computers. Therefore, obtaining sufficiently accurate approximations of complex curves was a very time consuming task. In most cases, builds were done manually. At the same time, in the region of a small Reynolds number, a significant underestimation of the experimental data is noticeable Computer calculations cannot be based on graphical data and requires a mathematical description. However, Altshul provided only a formula describing a fairly narrow range. In this paper, an approximation of the experimental data is proposed. The regions for which experimental data are absent are described on the basis of the assumptions made in this work. The results make it possible to simulate natural air exchange in the widest possible range of external factors.