Use calibration matrix to know CCD sensor size

Question

How can we know the camera sensor size from the calibration matrix?

I already have the calibration matrix. But the focal length is in pixels form.

Answer 1

The "focal length" in the calibration matrix is not actually expressed in pixels. It is in fact a ratio that relates the sensor size in the real world to the size of a pixel in the image. It relates the focal length of the lens to distances in the image using a scaling factor in each dimension. More details in this article.

Answer 2

As Zaphod says, you can get a decent approximation combining the calibration matrix with a known focal length for the lens in mm.

A more precise method: open the box, read the serial type number of the CCD, look it up on the interwebs. There are only a handful of CCD manufacturers, and they all publish their spec sheets on the web. Here is an example.