Gas Mileage Calculator

What Is a Gas Mileage Calculator?

A gas mileage calculator helps drivers determine their vehicle's fuel economy in miles per gallon (MPG), kilometers per liter (km/L), or liters per 100 kilometers (L/100km). It also helps estimate trip costs, driving range, and fuel requirements for any journey.

The fundamental formula is MPG = Distance / Fuel. By entering the distance traveled and fuel consumed, you get your vehicle's real-world fuel economy. The calculator also works in reverse: enter your MPG and fuel tank size to find your range, or enter distance and MPG to estimate fuel needed for a trip.

How to Use the Gas Mileage Calculator

Select what you want to calculate from the dropdown:

Solve for MPG — enter miles driven and gallons used to find fuel economy
Solve for Distance — enter MPG and fuel available to estimate driving range
Solve for Fuel Needed — enter distance and MPG to calculate gallons required
Solve for Trip Cost — enter distance, MPG, and fuel price to estimate total cost

Fuel Economy Units Explained

Three fuel economy conventions are in worldwide use:

MPG (US) — miles per US gallon, used in the United States. Higher is better.
L/100km — liters per 100 kilometers, the European standard. Lower is better.
km/L — kilometers per liter, used in Japan and parts of Latin America. Higher is better.

For distance-based cost estimation, check the Mileage Calculator and Fuel Consumption Converter for additional planning tools.

The calculator automatically converts between all three systems. For example, 25 MPG equals approximately 10.63 km/L or 9.41 L/100km.

The Formula

MPG = Distance (miles) / Fuel (gallons)

Related formulas:

Distance = MPG x Fuel (gallons)
Fuel = Distance (miles) / MPG
Trip Cost = (Distance / MPG) x Price per Gallon

How to Get Accurate MPG Readings

The most accurate way to measure fuel economy is the tank-fill method: fill the tank completely, reset the trip odometer, drive normally, then refill at the same pump. Divide the trip distance by the gallons displayed on the pump. Average 3-5 tanks for a stable real-world MPG figure, as single-tank numbers can vary by 10-20% due to weather, traffic, and driving conditions. You can also use our Fuel Cost Calculator to plan your trips more accurately.

Frequently Asked Questions

How do I calculate MPG?

Divide the miles driven by the gallons of fuel used: MPG = miles / gallons. For the most accurate result, use the tank-fill method: fill the tank completely, reset the trip odometer, drive normally, then refill and divide the trip distance by the gallons it took to top off.

How do I convert MPG to L/100km?

Use the formula L/100km = 235.215 / MPG (US). For example, 25 MPG = 235.215 / 25 = 9.41 L/100km. The conversion is exact and based on 1 US gallon = 3.78541 liters and 1 mile = 1.609344 kilometers.

What is a good MPG for a car?

For a modern sedan, 30+ MPG combined is solid and 40+ MPG is excellent. Compact hybrids routinely achieve 50+ MPG. SUVs and trucks typically run 18-25 MPG. Electric vehicles are rated in MPGe (miles per gallon gasoline-equivalent), with most modern EVs in the 100-130 MPGe range.

How much will a road trip cost in gas?

Use the formula: cost = (distance / MPG) x price per gallon. For example, a 300-mile trip in a 25 MPG car at $3.50 per gallon costs (300 / 25) x $3.50 = 12 gallons x $3.50 = $42.00. That works out to about $0.14 per mile.

Why is my real-world MPG lower than the EPA rating?

Real-world MPG averages 10-15% below the EPA combined figure for most cars. The gap widens with cold weather, short trips (engine never reaches operating temperature), aggressive driving, rooftop cargo (aerodynamic drag), and underinflated tires.

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