Most drivers believe that improving a car's fuel economy from 15 MPG to 20 MPG provides the same fuel savings as improving from 30 MPG to 35 MPG. Mathematically, this intuition is completely wrong.
The 'MPG Illusion' Explained
Miles Per Gallon measures distance per unit of fuel, which produces an inverse non-linear curve. To see the true financial impact, look at gallons consumed over 10,000 miles:
| Vehicle Upgrade | Fuel Used per 10,000 Miles | Gallons Saved | Money Saved (@ $3.75/gal) |
|---|---|---|---|
| 15 MPG → 20 MPG | 667 gal → 500 gal | 167 Gallons | $626.25 |
| 30 MPG → 35 MPG | 333 gal → 286 gal | 47 Gallons | $176.25 |
Replacing a 15 MPG gas guzzler with a 20 MPG vehicle saves more than 3.5 times as much fuel as upgrading from 30 to 35 MPG! This is why Europe and Canada use Liters per 100km (L/100km), which scales linearly with consumption.
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Frequently Asked Questions
What is the conversion formula between MPG and L/100km?
L/100km = 235.214 / MPG (US gallons). For example, 30 MPG = 235.214 / 30 = 7.84 L/100km.