Fuel Efficiency Calculator

EPA test cycles are conducted in laboratories under controlled temperature, with no air conditioning, no cargo load, and standardized driving patterns. Real-world factors that reduce MPG include: air conditioning use (can reduce MPG by 5–25%), driving at high speeds, stop-and-go traffic, cold weather (reduces MPG by 10–20% below 20°F), carrying heavy loads, roof racks, and aggressive driving habits. The EPA introduced revised testing in 2008 to be more realistic, but a gap often remains.

Fuel efficiency standards vary by vehicle class. For passenger cars: below 25 MPG is poor, 25–35 MPG is average, 35–45 MPG is good, above 45 MPG is excellent. Hybrid vehicles achieve 45–65 MPG, while plug-in hybrids can achieve equivalent efficiency of 80–100 MPGe. SUVs and trucks have lower benchmarks, with 20–25 MPG considered average for mid-size SUVs.

Yes. E10 gasoline (10% ethanol) reduces fuel economy by about 3–4% compared to pure gasoline, because ethanol contains less energy per gallon. E15 and E85 blends reduce efficiency further — E85 can lower MPG by 25–30%. Most pump gasoline in the US contains up to 10% ethanol, which is already factored into modern EPA estimates.

Calculating MPG at every fill-up is a best practice for vehicle maintenance awareness. Most modern vehicles and fuel apps track this automatically. Tracking over 5–10 fill-ups provides a reliable average. A sudden drop of 10% or more in MPG between fill-ups may indicate a mechanical issue and warrants a vehicle inspection.

Both measure the same thing from opposite perspectives. km/L (kilometers per liter) is a direct efficiency measure — higher is better, like MPG. L/100km (liters per 100 kilometers) measures consumption rate — lower is better. L/100km is preferred in Europe, Australia, and Canada because it scales linearly with fuel cost: if gas costs $1.50/L, a car using 8 L/100km costs exactly $12 per 100 km. Conversion: L/100km = 235.215 / (km/L).