Fuel Economy Calculator
Calculate fuel economy (MPG, L/100km), trip fuel cost, and compare vehicle efficiency. Convert between MPG and L/100km, and estimate annual fuel costs.
Fuel Economy
29.2
MPG
=
8.06
L/100km
Annual fuel cost
$1800.00
Annual gallons used
514.3 gal
Annual liters used
1947 L
Cost per mile
$0.1200
Cost per km
$0.0746
Gas price ($/L equiv)
$0.925
Annual Cost Comparison
Economy car (35 MPG)
$1500/yr$-300
Midsize sedan (28 MPG)
$1875/yr+$75
SUV (22 MPG)
$2386/yr+$586
Truck (18 MPG)
$2917/yr+$1117
Hybrid (50 MPG)
$1050/yr$-750
How to Use Fuel Economy Calculator
- 1Enter distance driven and fuel used (or MPG/L/100km directly).
- 2Set fuel price to calculate trip and annual fuel costs.
- 3Convert between MPG and L/100km for comparison.
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What is MPG and how is it calculated?▾
MPG (Miles Per Gallon) measures how many miles a vehicle travels on one gallon of fuel. MPG = Miles driven ÷ Gallons used. Example: drove 350 miles, used 12 gallons → MPG = 350/12 = 29.2 MPG. L/100km (liters per 100 kilometers) is used in most countries outside the US. L/100km = (Liters used × 100) ÷ Kilometers driven. Conversion: MPG ↔ L/100km: L/100km = 235.215 ÷ MPG (US gallons). Example: 30 MPG = 235.215/30 = 7.84 L/100km.
What is considered good fuel economy?▾
US averages (2023): New car average: ~28 MPG combined. Compact cars: 32–40 MPG. Midsize sedan: 28–35 MPG. SUVs: 20–30 MPG. Trucks: 15–25 MPG. Hybrids: 40–60 MPG. EVs: equivalent 90–130 MPGe. World context: EU average car: ~6–7 L/100km (≈40 MPG). Japanese Kei cars: 25–35 km/L. Corporate Average Fuel Economy (CAFE) standard US 2024: ~49 MPG combined. EPA ratings: city/highway/combined — highway is typically 15–30% better than city due to fewer stop-starts.
How does driving style affect fuel economy?▾
Aggressive driving (rapid acceleration, hard braking) can reduce fuel economy by 15–30% at highway speeds. Optimal speed: most vehicles peak efficiency at 50–60 mph; above 65 mph fuel economy drops significantly due to aerodynamic drag (drag ∝ v²). Air conditioning: reduces MPG by 5–25% in city driving. Cold starts: first few minutes after cold start are least efficient — engine runs rich. Tire pressure: underinflated by 10 PSI → ~1.5% fuel economy loss. Cargo weight: every 100 lb extra reduces MPG by ~1–2%. Highway vs city: city driving is 20–40% less efficient.
What is the difference between US and UK gallons?▾
US gallon: 3.785 liters. Imperial (UK/Canadian) gallon: 4.546 liters. This means UK MPG figures are ~20% higher than US MPG for the same fuel efficiency. A car rated 40 MPG (UK) = ~33 MPG (US) = 7.06 L/100km. Always specify which gallon when comparing across countries! Liters per 100km (L/100km) avoids this ambiguity — it's unambiguous regardless of country. The US EPA uses US gallons; UK Vehicle Certification Agency uses Imperial gallons.
How do I calculate fuel costs for a road trip?▾
Fuel cost = (Distance ÷ MPG) × Price per gallon. Example: 500-mile trip at 28 MPG with gas at $3.50/gallon → (500/28) × $3.50 = 17.86 gallons × $3.50 = $62.50. Metric: Cost = (Distance_km / 100) × L/100km × Price_per_liter. Example: 800 km trip at 8 L/100km with fuel at $1.50/L → (800/100) × 8 × $1.50 = $96. Annual fuel cost estimate: Assume 15,000 miles/year. At 28 MPG, $3.50/gal: (15,000/28) × $3.50 = $1,875/year. At 40 MPG: $1,313/year — saving $562 annually.