This calculator is designed to supply the area of any potential collection surface of any length and width in square feet and/or square inches, based on the length and width values entered in feet and inches, and the potential and estimated actual rainwater recovery in gallons.
It depends! Read the owner's manual for the brand of car you own or want to drive as each auto maker determines when to change the oil. Generally, I've read and experienced that full synthetic oil can last up to 5K-7500 miles, but... it also depends on other factors such as your driving style and where you live. VW has listed in its newer cars, like the 2015 VW Golf, that oil changes can be done in 10k miles!
If you are using a quality motor oil, changing it at 3-4000 miles is a waste of money. That is, of course is dependant upon the items mentioned above. A synthetic fluid should be good for 10K easily, providing the items mentioned above are good. The key is Filtration, Filtration, Filtration