1. The problem statement, all variables and given/known data I have a cylinder, for which i want to find the inertia tensor. http://www.mip.sdu.dk/~pino/inertiacyl.JPG Where the rotational axis are either the x (red) or y (green). 2. Relevant equations I know that the inertia tensor for a cylinder is of the form http://www.mip.sdu.dk/~pino/inertiamoment-cylinder.jpg Then I believe that the bottom right element stays the same, since this describes the rotation around the z-axis. The tricky part for me is the rest of the matrix. I am no expert, and do not understand inertia tensors fully, so I would like some pointers. 3. The attempt at a solution My immediate idea is that the matrix should remain in its diagonal form, the zeros will remain zeros, is this correct? I know that for complex forms i can split up the moments of inertia, so i have the moment of inertia for the blank space d, which is 0. and then i can add the moment of inertia of the cylinder, but how do i calculate this, when the rotational axis is x-axis for example?