Quote Originally Posted by RalphLambrecht View Post
or this for free:Attachment 45041
This paper pinhole calculator is great. I wish I had it year ago. There is similar one there : http://www.ilfordphoto.com/Webfiles/...6152612113.pdf

Please note that these calculators do not account for reciprocity failure.

And here is a chart for calculating pinhole sizes (i made it :-), sorry it is in french)