How much profit you've made from your ads compared with how much you've spent on those ads.
To calculate ROI, take the revenue that resulted from your ads, subtract your overall costs, then divide by your overall costs: ROI = (Revenue - Cost of goods sold) / Cost of goods sold.
Example
Let's say that you have a product that costs £100 to produce, and sells for £200. You sell six of these products as a result of advertising them. Your total sales are £1200, and your costs are £200. Your ROI is (£1,200-(£600+£200))/(£600+£200), or 50%.
To help measure your ROI, you'll need to track conversions, actions that you want your customers to take on your website after clicking your ad, such as a purchase, sign-up or download. Try conversion tracking or Google Analytics, free tools to help you track conversions in your account.
ROI is typically the most important measurement for advertisers because it shows the real effect that your ads have had on your business. While it's helpful to know the number of clicks and impressions that you get, it's even better to know how your ads are contributing to the success of your business.