1) Estimate your miles per gallon. The google can tell you this. Round down - give yourself an MPG - just to be safe 2) Research your fuel tank capacity (Also

1) Estimate your miles per gallon. The google can tell you this. Round down - give yourself an MPG - just to be safe 2) Research your fuel tank capacity (Also a google-able event) 2) Fill your tank completely 3) Reset your tripometer; drive until it nears the magic empty number: (Fuel Tank Capacity)x(Adjusted MPG). When it's within 10% of that number, you should consider adding more gas. If it's even closer to that number; you should really considering adding more gas. 4) Reset the tripometer every time you fill up