Fuel Economy Calculator
Calculate vehicle fuel economy across US MPG, UK Imperial MPG, kilometers per liter (km/L), and liters per 100 km (L/100km). Enter your distance traveled and fuel consumed to view instant fuel efficiency and driving cost per mile.
Calculate MPG, km/L, L/100km, and fuel costs with real-time updates
Equivalent to 38.21 UK Imperial MPG
MPG = Distance (mi) ÷ Fuel (gal)|L/100km = (Liters ÷ km) × 100How to Use This Fuel Economy Calculator
Enter Distance Driven
Input the odometer trip distance or route distance. Choose between miles or kilometers.
Enter Fuel Consumed
Enter the exact volume of fuel pumped. Choose US gallons, liters, or UK Imperial gallons.
Add Price (Optional)
Enter the fuel cost per gallon or liter to compute total fuel cost, cost per mile, and cost per km.
Fuel Economy Formulas & Calculation Engine
Exact mathematical relationships used for imperial and metric efficiency
Worked Example: Driving 350 miles and consuming 11 US gallons gives:350 ÷ 11 = 31.82 US MPG.
Worked Example: Using 40 liters to drive 500 kilometers gives:(40 ÷ 500) × 100 = 8.0 L/100km (12.5 km/L).
Understanding Fuel Economy Units: US MPG vs UK MPG
One of the most frequent sources of confusion in automotive efficiency comparisons is the difference between a United States liquid gallon and a United Kingdom Imperial gallon:
- 1 US Gallon = 3.78541 liters (231 cubic inches).
- 1 UK Imperial Gallon = 4.54609 liters (277.42 cubic inches), exactly 20.095% larger than a US gallon.
- Because the UK gallon contains more volume, a vehicle tested in the UK will travel roughly 20% farther per gallon. For example, 30.0 US MPG equals 36.03 UK MPG.
- Relying solely on dashboard computers: In-dash trip computers calculate fuel flow indirectly from injector pulse width. Studies demonstrate they often overestimate fuel economy by 3% to 7%.
- Mixing US and UK gallons: Comparing European automotive road test reviews directly to EPA window sticker numbers without converting gallons leads to false expectations.
- Assuming fuel consumption is linear: A drop from 50 to 40 MPG uses far less additional fuel than a drop from 20 to 15 MPG. Focus on total gallons saved rather than raw MPG jumps.
Frequently Asked Questions
Deep dive into formulas, odometer testing techniques, and conversion tables.
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