How do you calculate the ROI of 3D printing?

You can calculate the ROI of 3D printing by taking all the costs you make and drill it down to the costs of one part, and then compare it to how much you can sell it or how much it would cost to buy it somewhere else. You need to take in account the labour hours, the material costs, shipping costs, the 3D printer it self, maintenance, power of the machine etc.