I wrote CaliperTool to help. Enter a decimal inch value and press "calc." CaliperTool will find the closest 1/64" values above and below your measurement and print them along with their respective errors.

It will also do a simple metric conversion and list the measurement in millimeters.

And if that weren't enough, if your measurement is reasonably close to a "letter" or "number" drill bit size, it will list the closest of them as well.