Return on sales (ROS) is a measure of profitability that looks at how much net income a business earns for every dollar of sales. Return on investment (ROI) measures the performance of an investment by calculating the return on the cost of that investment. The main difference between these two metrics is their scope. ROS is narrowly focused (it only measures sales). ROI is a practical metric for just about any type of investment. It measures the returns of a specific project or venture on its own.