This video shows how to calculate ROI.
ROI, which stands for Return on Investment, is calculated by dividing income (profit) by the amount of capital invested. Thus, if a department of a large firm had income of $10 million and used $50 of capital, the ROI of the department would be 20%.
ROI is a frequently used measure of profitability. If two divisions of a firm have a similar level of profit but one of the divisions uses a lot more capital to achieve the profit, the ROI will show that the division achieving the same profit with less capital is making better use of its resources.