Here 
  
    
      
        Δ
        P
      
    
    {\displaystyle \Delta P}
   is the gas pressure difference across the barrier, 
  
    
      
        A
      
    
    {\displaystyle A}
   is the area of the hole, 
  
    
      
        
          N
          
            A
          
        
      
    
    {\displaystyle N_{A}}
   is the Avogadro constant, 
  
    
      
        R
      
    
    {\displaystyle R}
   is the gas constant and 
  
    
      
        T
      
    
    {\displaystyle T}
   is the absolute temperature.
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 
  
    
      
        A
      
    
    {\displaystyle A}
   on the container is punched to become a small hole, the effusive flow rate will be

where 
  
    
      
        M
      
    
    {\displaystyle M}
   is the molar mass, 
  
    
      
        
          N
          
            A
          
        
      
    
    {\displaystyle N_{A}}
   is the Avogadro constant, and 
  
    
      
        R
        =
        
          N
          
            A
          
        
        
          k
          
            B
          
        
      
    
    {\displaystyle R=N_{A}k_{B}}
   is the gas constant.