pixel to object mapping formula

Hi,

I forgot the formula.. something to do with tangent and radians.

Supposed I want to know how big a portion of object a certain distance
away would appear in a pixel in a camera.. with and without lens
magnification, what exact formula do you use?

Supposed the ccd chip resolution is 120x120 with pixel pitch of 25
micron.

And the focal length of the lens is 6.76 millimeters, with field of
view of 25 degrees and F-number of 1.5 with aperture of 4.5
millimeters.

How big in area of the an object say 5 meters away would appear to a
single pixel?

Thanks a lot.