§ 01 / TOOL
420 miles on 14 gallons.
STATUS ACTIVEUNIT US GALLATENCY <1MS
> INPUT
MODE MILES / GALLON
mi
PER
PER
gal
MPG.
FUEL ECON
// RESULT
30 MPG
// L / 100KM
7.84
// KM / L
12.75
// FORMULA
420 miles ÷ 14 gallons = 30 MPG
Driving 420 miles on 14 gallons is 30 MPG — roughly 7.84 L/100km or 12.75 km/L.
§ 02 / ABOUT
How fuel economy is measured.
Miles per gallon is distance divided by fuel: MPG = miles / gallons. Fill up, drive, fill up again, divide the trip miles by the gallons pumped the second time. That's it — and it's more accurate than the car's trip computer, which often flatters by 3–8%.
// WHAT SHIFTS YOUR MPG
- Speed — most gas engines peak around 50 mph. 75 mph burns 20–30% more fuel per mile.
- Acceleration and braking — jackrabbit starts and late braking both waste energy. Steady-state driving wins.
- Weight and drag — roof racks, full trunks, and open windows at highway speed all cost MPG.
- Temperature — cold engines run richer. Short winter trips can drop MPG by 15%.
// MPG VS L/100KM
The rest of the world uses liters per 100 km, which is a rate of consumption (lower is better) rather than a rate of travel. To convert, divide 235.215 by MPG. 30 MPG ≈ 7.84 L/100km. Use the Unit Converter for distance and volume.
Related: Auto Loan, Unit Converter, Percentage.
§ 02 / FAQ
Questions. Answered.
How is MPG calculated?+
Miles per gallon = miles driven ÷ gallons used. If you drove 350 miles on 12 gallons, that’s 350 ÷ 12 = 29.17 MPG. The number tells you how far the car travels on one gallon of fuel.
How do I measure real-world MPG?+
Fill up completely. Reset your trip odometer. Drive normally. Fill up completely again at the same pump if possible. Divide the miles shown on the trip odometer by the gallons it took to refill. Repeat over a few tanks for a stable average — single-tank readings swing with terrain and driving style.
Why the gap between EPA ratings and my real MPG?+
EPA tests are standardized laboratory runs. Real-world driving includes weather, traffic, cargo, tire pressure, aggressive acceleration, and highway speeds — all of which hurt fuel economy. Most drivers see 10–20% below EPA combined MPG. If you’re 30%+ below, check tire pressure and driving habits.
US gallon or UK gallon?+
US gallons (3.785 liters). UK gallons (4.546 liters) are about 20% larger, so UK MPG numbers are ~20% higher for the same fuel efficiency. If your figure came from a UK source, divide by 1.2 to convert roughly to US MPG.
What do the metric conversions mean?+
L/100km is the European standard — liters of fuel burned per 100 km driven. Lower is better (the opposite of MPG). km/L is the Japanese/Asian convention — kilometers per liter, higher is better. Both are shown so you can compare with spec sheets from any market.
Does the URL update so I can share?+
Yes. As you type, the URL updates to /mpg/350-12 (miles-gallons). Copy the URL bar or use the SHARE button.
§ 04 / TOOLS
Related calculators.
§ 05 / READING