Mpg Calculator
MPG (miles per gallon) is distance driven divided by fuel used: 320 miles on 11.5 gallons is 27.8 MPG. It is the headline number, but the number that decides your budget is cost per mile: fuel price divided by MPG. A 24-MPG car at $3.50 a gallon costs about $0.15 per mile, or roughly $1,875 a year at 12,500 miles. The calculator below computes MPG plus its metric equivalents (km/L and L/100 km), and, with an optional fuel price, your cost per mile and annual fuel bill.
MPG Calculator
Tip: enter both odometer readings and the distance is figured for you – no need to type the distance above.
Fuel economy:
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How to Measure MPG Accurately
Fill the tank completely, reset the trip odometer, drive normally, then fill completely again. Divide the trip miles by the gallons on the second fill. That brim-to-brim method beats trusting the dashboard, which is often optimistic by a few percent. One tank is noisy; average three or four for a reliable figure.
MPG, km/L, and L/100 km
MPG = miles / gallons. Metric drivers use km/L (higher is better, like MPG) or L/100 km (lower is better), where L/100 km = 235.21 / MPG. Our example: 27.8 MPG = 11.8 km/L = 8.5 L/100 km. Watch the gallon: a US gallon is 3.785 liters while an imperial gallon is 4.546, so a UK-quoted MPG figure is about 20% higher than the same car in US gallons.
What Counts as Good MPG
The average new gasoline car sits in the mid-20s MPG. Anything above 35 is very good; hybrids clear 45\u201357. Real-world results run 10\u201320% below EPA sticker figures because the tests do not include your commute, your right foot, or winter.
Five Things That Move Your Real MPG
Speed (fuel use climbs fast above 50 mph), tire pressure (a few PSI low costs measurable fuel), short cold trips, roof racks and cargo boxes, and aggressive acceleration and braking. Fixing the first two is free and immediate.
Frequently Asked Questions
How do I calculate MPG?
Divide miles driven by gallons used: 320 miles / 11.5 gallons = 27.8 MPG. Measure brim-to-brim for accuracy.
How do I convert MPG to L/100 km?
L/100 km = 235.21 / MPG (US gallons). So 27.8 MPG = 8.5 L/100 km.
What is a good fuel economy in 2026?
Mid-20s MPG is average for a new gasoline car, 35+ is very good, and hybrids reach 45\u201357 MPG.
Why is my real MPG lower than the sticker?
EPA figures come from standardized lab tests. Real driving adds cold starts, traffic, speed, weather, and load, typically costing 10\u201320%.
Does premium fuel improve MPG?
Only if your engine requires it. Engines designed for regular gain almost nothing from premium, and the price premium wipes out any tiny gain.
How much does speeding cost in fuel?
Fuel economy falls roughly 7% for each 5 mph above 50 mph, so cruising at 75 instead of 55 can cost 15\u201320% more fuel.
Odometer input and unit converter
Two new input paths make the tool faster. Odometer mode: type your starting and ending odometer readings and the distance is computed for you - handy when you filled up between readings and never noted the trip distance. Converter mode: switch the mode selector to convert any fuel-economy figure between MPG, L/100 km, and km/L. For example, 30 MPG = 7.84 L/100 km = 12.75 km/L. The math: L/100 km = 235.215 / MPG, and km/L = 100 / (L/100 km).