- The percentage of budget spent compared to how many forms were completed
- The number of clicks your ad received divided by the number of times it showed
- How much you’ve spent on the campaign compared to the value of leads generated
- You can’t calculate return on investment for campaigns that are focused on online leads
Explanation: How much profit you’ve made from your ads compared to how much you’ve spent on those ads. Return on investment (known as ROI) measures the ratio of your profits to your advertising costs.
Read more here: https://support.google.com/adwords/answer/14090?hl=en