Sharpening doesn’t really fix focus. It adjusts edge contrast.
There is a calculator here: http://www.dofmaster.com/dofjs.html and here: http://www.cambridgeincolour.com/tutorials/dof-calculator.htm
For Canon shooters, there is a Canon version here: http://cpn.canon-europe.com/content/education/technical/depth_of_field_calculator.do I haven’t tried it yet.
Android app: https://play.google.com/store/apps/details?id=jds.dofcalc&hl=en A complaint is that there is no APS-C option, just full frame. I think a crop sensor does not change focal length, and can demonstrate using full frame or crop body with the same lens does not change DOF enough to matter. I use the same full frame camera with the dofmaster calculator for all calculations, regardless of the actual body I’m using. Really, understanding the general concepts is more important than dragging out a calculator for every shot.