Gas Mileage Calculator Fuel Economy
Gas Mileage Calculator
Trip Information
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Fuel Efficiency
Distance Traveled
12.50 gal consumed
Trip Fuel Cost
$0.00 per mi
Est. Annual Fuel Cost
Based on 0 mi/year
CO₂ Emissions
Carbon dioxide for this trip
Inverse Efficiency
Fuel consumption rate
Vehicle Efficiency Comparison
Gas mileage (MPG) tells you how many miles your vehicle travels per gallon of fuel. Calculating your actual MPG from your fill-ups is more accurate than EPA estimates, which often do not reflect real-world driving. This calculator finds your MPG from odometer readings and gallons pumped, and converts between MPG and L/100km.
How to Calculate Your Actual MPG
Fill up completely, note the odometer, drive for a full tank, fill up again completely, note gallons purchased and new odometer reading. Your actual MPG = miles driven / gallons used.
MPG = Miles Driven / Gallons Used Miles Driven = New Odometer - Previous Odometer Conversions: MPG to L/100km: 235.2 / MPG L/100km to MPG: 235.2 / (L/100km)
Example: 12,450 - 12,075 = 375 miles driven. 13.5 gallons pumped. MPG = 375/13.5 = 27.8 MPG.
Factors That Affect Gas Mileage
Your actual MPG varies from the EPA estimate based on driving style, conditions, and maintenance. Understanding these factors helps you improve efficiency.
| Factor | Effect on MPG |
|---|---|
| Highway vs city driving | Highway usually 25-30% better |
| Speed over 50 mph | -2% per 5 mph above 50 |
| Cold weather | -15 to -25% in extreme cold |
| Air conditioning | -5 to -25% |
| Underinflated tires | -0.2% per 1 psi below optimal |
| Roof rack (empty) | -5% |
| Aggressive driving | -15 to -30% |
Frequently Asked Questions
Why is my real MPG worse than the EPA estimate?⌄
EPA tests are conducted under controlled conditions. Real-world driving involves more variables: cold starts, short trips (engine never reaches optimal temperature), aggressive acceleration, air conditioning, hills, headwinds, and highway speeds above the test protocol. Expect real-world MPG to be 10-20% below the EPA estimate as a normal range.
How can I improve my gas mileage?⌄
Keep tires properly inflated (check monthly). Use the recommended motor oil grade. Remove unnecessary weight. Avoid excessive idling. Drive at steady speeds (cruise control on the highway). Anticipate stops and coast to reduce braking. Reduce AC use. Keep up with engine maintenance (air filter, spark plugs). These combined changes can improve MPG by 10-20%.
What is the difference between MPG and L/100km?⌄
MPG (miles per gallon) is used in the US and UK. L/100km (liters per 100 kilometers) is used in most of the rest of the world. Higher MPG is better (more distance per unit of fuel). Lower L/100km is better (less fuel per unit of distance). They are inversely related: 30 MPG ≈ 7.84 L/100km.
Does ethanol content in fuel affect MPG?⌄
Yes. E10 (10% ethanol, standard in most US gas) reduces MPG by about 3-4% compared to pure gasoline because ethanol contains less energy per gallon. E15 and E85 show proportionally larger reductions. Regular E10 is the baseline for most fuel economy discussions, but some premium fuels with very low ethanol content can improve MPG slightly.