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About This Calculator
Gas mileage, or fuel economy, measures how far a vehicle travels per unit of fuel and is the most practical indicator of a car's operating efficiency. This calculator computes miles per gallon or liters per 100 kilometers from your odometer readings and fuel fill-up amounts over one or more tanks. Tracking fuel economy over time reveals maintenance issues like underinflated tires or failing oxygen sensors before they become expensive repairs.
Quick Tips
- 1 Fill your tank completely, reset the trip meter, and refill to measure true MPG.
- 2 Aggressive acceleration reduces gas mileage by up to 33% on highways.
- 3 Track MPG over 3+ fill-ups for an accurate average, not just one tank.
Example Calculation
Car traveled 382 miles on 14.5 gallons of gas.
Fuel economy: 26.34 MPG | 11.19 km/L | 8.94 L/100km | Cost at $3.50/gal: $0.133/mile
How to Calculate Your MPG
Divide the miles driven by the gallons of fuel used. For the most accurate reading, fill your tank completely, reset your trip odometer, drive normally, then fill up again and record the gallons. Your MPG is the trip miles divided by the gallons pumped.
MPG vs Liters per 100km
The US uses miles per gallon (MPG), while most other countries use liters per 100 kilometers (L/100km). To convert MPG to L/100km, divide 235.215 by the MPG value. Higher MPG is better; lower L/100km is better.
Factors That Affect Gas Mileage
Key factors include driving style (aggressive driving reduces MPG by 15-30%), vehicle maintenance, tire pressure, weather (cold weather reduces MPG), terrain (hills reduce MPG), cargo weight, and use of air conditioning.
Tracking Your Fuel Economy
Track your MPG over multiple fill-ups to get an accurate average. A sudden drop in fuel economy can indicate a maintenance issue like underinflated tires, a dirty air filter, or an engine problem that needs attention.
Frequently Asked Questions
For passenger cars, 30+ MPG is good and 40+ MPG is excellent. For SUVs, 25+ MPG is good. For trucks, 20+ MPG is good. Hybrid vehicles typically achieve 40 to 60 MPG, and plug-in hybrids can exceed 100 MPGe.
EPA ratings are based on standardized tests. Real-world MPG is often 10% to 20% lower due to aggressive driving, city traffic, short trips, cold weather, and use of accessories like A/C. Highway driving usually comes closest to the rating.
Divide 235.215 by your MPG value. For example, 30 MPG equals 235.215 / 30 = 7.84 L/100km. This calculator performs the conversion automatically.
Yes. E10 (10% ethanol) reduces MPG by about 3% compared to pure gasoline. E15 (15% ethanol) reduces it by about 4-5%. E85 (85% ethanol) reduces MPG by 20-30%. Ethanol contains less energy per gallon than gasoline.