Gas Mileage Calculator (MPG & L/100km)
Calculate fuel economy in MPG (miles per gallon) or L/100km from distance driven and fuel used. Converts between both standards.
What this calculates
Fuel economy is the most-tracked car metric. The US, UK (mpg, but UK gallons differ), and many other countries use miles per gallon; most of the world uses liters per 100 kilometers. This calculator computes both from your trip data and converts between the two standards.
Formula & how it works
MPG (US) = miles ÷ gallons. MPG (UK) = miles ÷ (US gallons × 0.832674). L/100km = (liters ÷ km) × 100. Conversions: L/100km = 235.215 ÷ MPG (US); MPG (US) = 235.215 ÷ L/100km. The asymmetry is because MPG is 'distance per fuel' (higher is better) while L/100km is 'fuel per distance' (lower is better).
Worked example
Drove 350 miles, used 12 US gallons. MPG = 350 ÷ 12 = 29.17 MPG. In metric: 350 mi = 563.27 km, 12 gal = 45.42 L, so 45.42 ÷ 563.27 × 100 = 8.06 L/100km. Quick check: 235.215 ÷ 29.17 ≈ 8.07 L/100km ✓.
Frequently asked questions
Why does my real mileage differ from the EPA sticker?
Sticker numbers come from controlled lab tests. Real driving involves cold starts, traffic, weather, terrain, payload, AC use, and driving style. Most people see 80–95 % of the sticker. Trip computers can also be ~2–5 % optimistic.
How can I improve my MPG?
Steady speeds under 65 mph, gentle acceleration, proper tire pressure, less idle time, and dropping unused roof racks/cargo. Combined these can lift real-world MPG by 10–20 %.
Is hybrid math the same?
Yes for ICE-only operation. For plug-in hybrids, you'd typically track MPGe (miles per gallon equivalent), which equates electricity consumption to gallons of gasoline.
Why do European cars seem more efficient?
Smaller engines, diesel availability, manual transmissions, lower speed limits, and more compact cars. The same Toyota model often gets better MPG in EU spec than US spec for these reasons.