There is little need for pinhole diameter accuracy finer than several percent, even for critical pinhole photography. There is nearly a 2:1 ratio between the largest and smallest diameter pinholes commonly used for each focal length. Nor do the popular pinhole diameter calculators closely agree. Carefully made by hand pinholes can be as clean and accurate as laser drilled ones. More important is selecting the correct diameter for the focal length, color of the light used, angle of coverage, and magnification ratio.
Originally Posted by Rich Ullsmith