How many people will come to your website? For the most accurate data, pull a monthly view of Sessions from Google Analytics to populate this field. Or, put some realistic traffic goals in place to see how it effects your bottom line after you’ve inputted metrics into the other fields.
This is an important metric you should monitor closely. The secret here is having good communication between marketing and sales.
Use the average sale amount of one of your products or services as a metric here.
Finally, factor in how much you pay for SEO each month. When you combine how much you make with how much you pay in SEO costs, you can then see the potential monetization and SEO ROI.