Pixel Size (width and height) calculation formula

I am trying to use the camera matrix to find the location of pixels forming a certain object in an image. Two parameters that I need to calculate, the length and with of the pixel in the image.

As I am working on the synthetic environment (3d max) I have access to: focal length, size of the sensor and resolution of the output image.

I am struggling to find the size of the pixel and already contacted Autodesk support team but no change so far. If anyone can help with the formula of calculating the pixel size I would be grateful. thanks