I have used the moment of inertia function in BoneJ to calculates the second moments of area for a set of thresholded cortical bone slices. I am most interested in the second moment of area values around the longest and shortest principal axes (I_1, I_3). The units of these parameters are given in kg*m^2, but I would like to convert them to mm^4. I made a calibration image consisting of a white rectangle of dimension 300 x 100 on a black background, with a line width of 1 pixel. I used BoneJ to calculate the moments around the axes and was hoping to use the calibration factor of 1.8 g/cm^3 and work backwards to convert the results to paper calculations of a rectangle with the same dimensions. Unfortunately I have not been successful at the conversion after many attempts.

My paper calculations are using the formula for a hollow rectangular section listed here (https://skyciv.com/tutorials/area-moment-of-inertia-equations/). BoneJ gave results of 19200.48 kg*m^2 for I_1 and 3000.3 kg*m^2 around I_3.