Calculate trip fuel cost, cost per mile or kilometre, and your annual fuel spend. Compare two vehicles to see how much you'd save by switching.
The formula is straightforward: divide the distance by your fuel economy to get fuel used, then multiply by the price per unit of fuel. For example, a 300-mile trip in a car getting 30 MPG uses 10 gallons — at $3.50/gallon, that's $35.00.
MPG (miles per gallon) is used in the US — higher is better. L/100km (litres per 100 kilometres) is used in most other countries — lower is better. To convert: L/100km = 235.215 ÷ MPG.
The savings from better fuel economy are significant over time. A car getting 40 MPG vs 25 MPG saves over $700 per year at 12,000 miles and $3.50/gallon — that's over $7,000 across a 10-year ownership period, not counting future price increases.
Use the formula: L/100km = 235.215 ÷ MPG. So 30 MPG = 235.215 ÷ 30 = 7.84 L/100km. To go the other way: MPG = 235.215 ÷ L/100km.
For a typical petrol (gasoline) car, 30–40 MPG (7–8 L/100km) is considered efficient. Hybrids typically achieve 45–55 MPG (4–5 L/100km). SUVs and trucks are usually 20–28 MPG (8–12 L/100km). Electric vehicles are excluded from this measure as they use kWh/100km or MPGe instead.
Cost per mile = fuel price ÷ MPG. At $3.50/gallon and 30 MPG, that's $3.50 ÷ 30 = $0.117 per mile (~11.7 cents). This is the fuel portion only — total cost per mile including depreciation, insurance, and maintenance is typically 3–5× higher.