AUTO CALCULATOR
Gas Mileage Calculator
Calculate your real-world gas mileage from distance and fuel used. Convert the result to MPG, L/100 km, km/L and miles per liter, then estimate trip and annual fuel costs.
Enter Your Trip Details
Calculate MPG, fuel consumption and trip cost from real driving data.
Trip data
Fuel cost
Annual driving estimate
Tip: use a full-tank-to-full-tank measurement over several hundred miles or kilometers for a more reliable real-world result.
Your mileage results will appear here
Enter a distance and the fuel used, then select Calculate Mileage.
What Is Gas Mileage?
Gas mileage describes how far a vehicle travels for a given amount of fuel. In the United States it is commonly expressed as miles per gallon (MPG), while many other countries use liters per 100 kilometers (L/100 km). Our fuel economy conversion tool converts between these measurements, while this calculator starts with the distance you actually drove and the fuel you actually used.
Measuring your own mileage is useful because real driving conditions rarely match laboratory testing. Traffic, temperature, hills, tire pressure, payload, air conditioning and driving habits can all affect fuel consumption. For a broader ownership estimate, combine this result with the Fuel Cost Calculator.
How to Calculate Gas Mileage
The basic MPG calculation is straightforward: divide the miles driven by the gallons of fuel consumed. If you use kilometers and liters, the equivalent consumption calculation is liters divided by kilometers, multiplied by 100.
Gas Mileage Calculation Reference
| Measurement | Formula | Better direction |
|---|---|---|
| US MPG | Miles ÷ US gallons | Higher is better |
| L/100 km | Liters ÷ kilometers × 100 | Lower is better |
| km/L | Kilometers ÷ liters | Higher is better |
| miles/L | Miles ÷ liters | Higher is better |
How to Get an Accurate MPG Measurement
The most practical method is the full-tank method. Fill the tank, reset the trip odometer, drive normally, then refill the tank and record how much fuel was added. Divide the distance shown on the trip meter by the fuel added. Repeating this over several tanks generally gives a more useful picture than measuring a single short trip.
- Fill the tank to the same practical stopping point.
- Reset the trip odometer or record the starting odometer reading.
- Drive normally and record the distance traveled.
- Refill the tank and record the fuel added.
- Divide distance by fuel used to calculate MPG.
MPG vs. L/100 km: Which Is Better?
MPG and L/100 km describe the same idea from opposite directions. MPG tells you how far a vehicle can travel on one gallon, so a higher number means better efficiency. L/100 km tells you how much fuel is required to travel 100 kilometers, so a lower number means better efficiency. This difference is important when comparing vehicles across countries.
For example, improving from 25 MPG to 30 MPG is an improvement, while reducing consumption from 9.4 L/100 km to 7.8 L/100 km is also an improvement. Use the unit comparison tool for a direct conversion.
Fuel Cost From Gas Mileage
Once you know MPG, fuel cost can be estimated by dividing the distance by MPG to find gallons used, then multiplying gallons by the fuel price. This is especially useful for comparing commuting costs, road trips and different vehicles.
Fuel is only one part of vehicle ownership. If you are shopping for a vehicle, compare fuel expense alongside the purchase price and financing. Our Car Affordability Calculator can help estimate a vehicle price from a monthly budget, while the Car Payment Calculator focuses on financing.
Why Your Real-World Mileage Changes
Gas Mileage for City and Highway Driving
City and highway mileage can differ substantially because urban driving involves more acceleration, braking and idling. Highway driving at a steady speed may use less fuel per mile, although very high speeds can also reduce efficiency. When tracking your vehicle, keep separate notes for city-heavy and highway-heavy trips if you want to understand your driving pattern.
Worked Example
Suppose a vehicle travels 300 miles and uses 10 US gallons. Its estimated gas mileage is 300 ÷ 10 = 30 MPG. That corresponds to about 7.8 L/100 km and about 12.8 km/L. At $3.50 per gallon, the trip costs about $35 in fuel, before parking, tolls or other travel expenses.
| Input or result | Example |
|---|---|
| Distance | 300 miles |
| Fuel used | 10 US gallons |
| Gas mileage | 30 MPG |
| Fuel consumption | About 7.8 L/100 km |
| Fuel price | $3.50/gal |
| Trip fuel cost | $35.00 |
How to Improve Gas Mileage
Smooth acceleration, avoiding unnecessary idling, maintaining appropriate tire pressure, reducing unnecessary cargo and keeping the vehicle properly maintained can all help. Route planning can also matter: a slightly longer route with steady traffic may sometimes consume less fuel than a shorter route with heavy stop-and-go traffic.
If you want to compare the financial effect of efficiency improvements, run the same distance through this calculator using different MPG values. For example, compare a current vehicle with a more efficient replacement before making a purchase decision.
Gas Mileage vs. Fuel Economy
The terms are closely related, but they are often used differently. Gas mileage usually refers to the measured distance a particular vehicle travels per amount of fuel. Fuel economy is the broader efficiency concept and is commonly reported as MPG or L/100 km. For unit conversions and side-by-side efficiency measurements, see the fuel economy converter.
Common Gas Mileage Mistakes
- Mixing US gallons with Imperial gallons.
- Using the dashboard's instantaneous MPG as a long-term measurement.
- Measuring over a very short distance.
- Forgetting that fuel added at the next fill-up is the fuel consumed during the measurement period.
- Comparing MPG numbers without checking whether they are US or UK MPG.
- Assuming advertised fuel economy will exactly match real-world driving.
Gas Mileage Calculator FAQs
How do I calculate MPG?
Divide the miles driven by the US gallons of fuel consumed. For example, 300 miles divided by 10 gallons equals 30 MPG.
Is higher MPG better?
Yes. A higher MPG number means the vehicle travels farther on each US gallon. For L/100 km, the opposite is true: a lower number means less fuel is needed.
How accurate is a gas mileage calculation?
Accuracy depends on how accurately distance and fuel use are measured. A full-tank measurement repeated over several tanks can reduce the effect of small measurement differences.
Why is my actual MPG lower than the advertised MPG?
Advertised ratings are based on standardized testing. Traffic, weather, speed, terrain, payload, tire pressure and driving habits can make actual mileage different.
What is a good MPG?
There is no single good MPG number for every vehicle. A small hybrid and a large pickup have very different expected fuel-economy ranges. Compare vehicles in the same class and driving conditions.
What is L/100 km?
L/100 km means liters of fuel consumed to travel 100 kilometers. Unlike MPG, lower L/100 km indicates better fuel efficiency.
Can I calculate fuel cost from MPG?
Yes. Divide the distance by MPG to estimate gallons used, then multiply by the fuel price per gallon. This calculator performs that calculation for you.
Should I use city or highway MPG?
For a real-world calculation, use the distance and fuel actually measured for your trip. If you are comparing published ratings, keep city and highway figures separate.