Embrace the fact that you won’t get the exact number right.
But make sure to get the order of magnitude correct. Should you be getting 50, 500, 5000, 50,000 customers?
If you get 30,000 page views, 6,000 clicks and 50 customers what that’s a good marketing return on investment?
Once you have mastered being able to do quick < 5 mins back of the envelope calculations, the you can make decisions faster and more accurately