The MPG field in this template is a calculated field — it runs the arithmetic automatically from total miles driven and gallons filled. That's significant because manual MPG tracking is where most fuel logs fail: people either forget to calculate it or calculate it wrong by forgetting to track miles between fill-ups consistently. The formula is straightforward but requires two accurate inputs every time, and it only produces a meaningful number if you're filling the tank to the same level at each stop.
What Fuel Consumption Data Actually Tells You
Real-world fuel economy is a diagnostic tool. The vehicle manufacturer's EPA estimate is a controlled condition number. Your actual MPG over six months of real-world driving — winter cold starts, summer A/C load, city versus highway mix, tire pressure, load weight, ethanol blend seasonal variation — is the number that matters for budgeting and for catching problems early.
A fuel economy drop of 8-10% sustained over multiple consecutive fill-ups is the signature of several developing issues: a failing oxygen sensor, clogged fuel injectors, spark plugs past service life, air filter restriction, or a cooling system problem causing the engine to run rich while warming up. Catching that drop at fill-up seven instead of fill-up twenty means you address it before it compounds into a larger repair.
This database keeps two vehicles in the dropdown: a 2006 Saturn Vue and a 2008 Toyota Sienna. Two vehicles tracked in one database means fuel economy comparisons across the household fleet, and clear visibility into which vehicle is actually cheaper to operate per mile — which often isn't the one with better EPA ratings once real-world driving patterns are factored in.
Cost per Mile is the field that connects fuel economy to actual transportation economics. A vehicle getting 24 MPG with fuel at $3.80 per gallon is running at approximately $0.158 per mile in fuel costs. A vehicle getting 19 MPG at the same price is running at $0.20 per mile. On 15,000 miles per year, that gap is $630 in annual fuel spend — a number that's invisible without the calculation but obvious once tracked.
Location logging is for the driver who noticed the 2006 Saturn Vue consistently posted better MPG when filled at one gas station versus another — which, occasionally, is a real phenomenon tied to ethanol blend percentages that vary by region and supplier.