Circle of confusion calculator.
Choose a camera maker, then a camera model.
At the right you will see a circle of confusion calculated for the camera.
To copy data to a desired dof calculator line click the link next to circle of confusion or just copy-paste.
"Digital" approach to calculations - it takes a least side size of the 2 photo-sites of a sensor.
Two, because on cameras with Bayer filter 1 pixel is created by a square of 2x2 photo-sites.
Safety coefficient is just an additional multiplier for the results.
"Classic approach" - this way ignores the size of photo-sites and number of megapixels completely.
Instead it's using only the sensor's diagonal. Older standard says it should be divided by 1000,
newer says it should be divided by 1500. In reality, if you work with a digital image, if you crop and
magnify, this way of calculations becomes absolutely meaningless, but many people still like it.
You can read more about this method here: http://en.wikipedia.org/wiki/Zeiss_formula,
And much more here (chapter: "The diameter of the circle of confusion"):
Depth of Field and Bokeh