The formula for measuring roi is (Gain from Investment – Cost of Investment) / Cost of Investment.
Identify what your CTR is. This refers to the click through rate, meaning how many customers clicked on your website after seeing it in the search engine results. Then, take a look at your conversion rates and how much they have increased or decreased according to the goal you had in mind. Figure out the value of each of these conversion goals you have met. Moreover, you should also measure the amount of organic traffic that has been coming to your website and which position you have been ranking in search page results. It is also important to measure any revenue you have generated through clicks or views. Then use the formula to estimate ROI.