How to Use This Gas Mileage Calculator
This gas mileage calculator helps you determine your vehicle's fuel efficiency in both US (MPG) and metric (L/100km) units. You can also estimate your trip cost by entering the fuel price per gallon or liter.
Steps:
- Enter the distance you traveled (miles or km)
- Enter the amount of fuel used (gallons or liters)
- Optionally, enter the fuel price to estimate trip cost
- View your MPG, L/100km, and cost breakdown
MPG vs. L/100km Explained
MPG (Miles Per Gallon) is used primarily in the United States and measures how many miles a vehicle can travel on one gallon of fuel. A higher MPG means better fuel efficiency.
L/100km (Liters per 100 Kilometers) is the standard metric measurement used in most of the world. It measures how many liters of fuel a vehicle consumes to travel 100 kilometers. A lower L/100km means better fuel efficiency.
Note that the two scales work in opposite directions: higher is better for MPG, while lower is better for L/100km.
| MPG | L/100km | Efficiency Rating |
|---|---|---|
| 10 – 15 MPG | 23.5 – 15.7 L/100km | Poor |
| 15 – 25 MPG | 15.7 – 9.4 L/100km | Below Average |
| 25 – 35 MPG | 9.4 – 6.7 L/100km | Average |
| 35 – 45 MPG | 6.7 – 5.2 L/100km | Good |
| 45+ MPG | Below 5.2 L/100km | Excellent |
How to Calculate Gas Mileage
MPG formula:
MPG = distance (miles) ÷ fuel used (gallons)L/100km formula:
L/100km = (fuel used in liters ÷ distance in km) × 100Conversion between MPG and L/100km:
L/100km = 235.215 ÷ MPG MPG = 235.215 ÷ L/100kmExample: You drove 300 miles and used 12 gallons of gas. MPG = 300 ÷ 12 = 25.0 MPG. Converting: L/100km = 235.215 ÷ 25.0 = 9.4 L/100km.
Tips to Improve Fuel Efficiency
- Maintain steady speeds. Use cruise control on highways. Aggressive acceleration and braking can reduce fuel efficiency by 15–30% at highway speeds.
- Keep tires properly inflated. Under-inflated tires increase rolling resistance and can reduce MPG by up to 3%.
- Remove excess weight. Every 100 lbs of extra weight reduces MPG by about 1%. Remove unnecessary cargo from your vehicle.
- Get regular maintenance.Replace air filters, spark plugs, and oil according to your manufacturer's schedule.
- Reduce idling. Idling gets 0 MPG. Turn off your engine if you expect to wait more than 60 seconds.
- Use the right fuel. Use the octane level recommended by your manufacturer. Premium fuel in a regular-gas car offers no benefit.
Real-World Examples
Example 1 — Daily Commute: You fill up with 10.5 gallons and reset your trip meter. After a week of commuting, your odometer shows 378 miles. MPG = 378 ÷ 10.5 = 36.0 MPG (L/100km = 6.5).
Example 2 — Road Trip Cost: Road trip of 450 miles using 18 gallons at $3.50/gallon. MPG = 25.0, Total cost = 18 × $3.50 = $63.00, Cost per mile = $0.14.
Frequently Asked Questions
How do I accurately measure my fuel consumption?
The most accurate method is to fill your tank completely, reset your trip odometer to zero, drive normally until you need fuel again, then fill the tank completely again. The number of gallons needed to refill equals the fuel used, and the trip odometer shows the distance traveled.
Why does my MPG vary between fill-ups?
MPG varies due to driving conditions (city vs. highway), weather (cold weather reduces efficiency), traffic, vehicle load, tire pressure, and fuel quality. For a more accurate picture of your vehicle's efficiency, calculate MPG over several fill-ups and take the average.
What is a good MPG for a car?
For a typical sedan, 25–35 MPG is average, 35–45 MPG is good, and 45+ MPG is excellent. SUVs and trucks typically get 15–25 MPG. Hybrid vehicles often achieve 40–60 MPG, and electric vehicles are rated in MPGe (miles per gallon equivalent).
Does driving faster use more fuel?
Yes. Fuel efficiency typically decreases significantly above 50 mph. At highway speeds, each 5 mph over 50 mph is like paying an additional $0.20–$0.30 per gallon. Aerodynamic drag increases exponentially with speed, making fuel efficiency drop faster at higher speeds.
How accurate is the trip cost estimate?
The trip cost estimate is based on the fuel consumed and the price you enter. It provides a good approximation but doesn't account for variations in fuel price between stations, idling losses, or detours. For budgeting purposes, it's best to use a slightly higher fuel price than you expect to pay.
Can I use this for a diesel vehicle?
Yes. The formulas work the same for gasoline and diesel vehicles. Diesel engines typically achieve 20–35% better fuel economy than gasoline engines, though diesel fuel is often slightly more expensive per gallon.