Effusion from an equilibrated container into outside vacuum can be calculated based on kinetic theory. The number of atomic or molecular collisions with a wall of a container per unit area per unit time (impingement rate) is given by:
assuming mean free path is much greater than pinhole diameter and the gas can be treated as an ideal gas.
If a small area  on the container is punched to become a small hole, the effusive flow rate will be
where  is the molar mass,  is the Avogadro constant, and  is the gas constant.
The average velocity of effused particles is
Combined with the effusive flow rate, the recoil/thrust force on the system itself is
An example is the recoil force on a balloon with a small hole flying in vacuum.