Hey. So you're trying to figure out your car's gas mileage, or maybe you're comparing cars and the numbers don't make sense. One ad says "30 MPG," another says "7 L/100km." Which is better? If you're traveling or moving countries, this stuff gets confusing fast.

I built this Fuel Economy Calculator because I was constantly doing the math in my head (and usually getting it wrong). It's a simple tool that converts between all the different ways countries measure fuel efficiency. You put in a number, pick the units, and instantly see what it means in any other system.

What This Tool Is For

It converts between the four main fuel economy units used around the world:

  • Miles per Gallon - US (MPG): Used in the United States. How many miles you can drive on one US gallon of fuel.
  • Miles per Gallon - UK (MPG): Used in the United Kingdom. Beware! A UK gallon is larger than a US gallon, so the number is different for the same efficiency.
  • Liters per 100 Kilometers (L/100km): Used in Europe, Canada, Australia, China, and most of the world. How many liters of fuel it takes to drive 100 km.
  • Kilometers per Liter (km/L): Used in Japan, India, and some other countries. How many kilometers you can drive on one liter of fuel.

The tool works both ways. You can start with any unit and convert to any other.

The Big Confusion: MPG vs. L/100km

This is the core problem. The US uses MPG (miles per gallon), which is a "bigger is better" measure. More miles per gallon = more efficient.

Most of the world uses L/100km (liters per 100km), which is a "smaller is better" measure. Fewer liters per 100 km = more efficient.

Your brain has to flip the logic depending on the unit. This tool does that for you. You'll see that a good, efficient car might be 35 MPG (US) OR 6.7 L/100km.

How to Use the Calculator

It's a two-panel converter. Very intuitive.

Step 1: The "From" Side (Left Panel)

Type the fuel economy value you know into the top box. Then, select its unit from the dropdown menu below. For example, if your American car's sticker says "28", type that and select Miles per Gallon (US).

Step 2: The "To" Side (Right Panel)

The right side updates automatically. The result shows the equivalent fuel economy. The dropdown on the right shows what unit it's displayed in. By default, it's set to Liters per 100km, the global standard. You can change this dropdown to any other unit you want to see.

Two-Way Magic: You can also start from the right side! If you know a car uses 5 L/100km, type "5" on the right, select "Liters per 100km," and the left side will show you that's about 47 MPG (US).

Who Is This For?

Anyone who deals with cars, fuel, or travel across borders.

  • Car Shoppers: Comparing fuel efficiency of US imports vs. European models.
  • Travelers & Expats: Renting a car abroad and trying to understand the local fuel efficiency ratings or calculate trip costs.
  • Fleet Managers: Managing vehicles with specs from different regions.
  • Environmentalists & Data Nerds: Comparing the efficiency of vehicles globally.
  • Students: Learning about units, conversions, and energy efficiency.
  • Everyday Drivers: To finally understand what those numbers on the window sticker or in a review actually mean.

The Real Value: Making Informed Decisions

When you're buying a car, a difference of 5 MPG might not sound huge. But convert it to L/100km, and you can calculate the actual fuel cost over a year. You might find that the "slightly less efficient" car costs hundreds of dollars more per year in fuel. This tool gives you the numbers to make that comparison fairly, even if the cars are rated in different systems.

It also prevents the "UK vs. US MPG" trap. A British car magazine might rave about a new model getting "60 MPG." An American reader might think that's impossible. But convert that UK MPG to US MPG, and it's about 50 MPG—still great, but not a miracle. The tool handles this gallon difference automatically.

Practical Examples

  • Buying a used import: You see a Japanese import rated at 15 km/L. Is that good? Convert to L/100km: ~6.7 L/100km. Convert to US MPG: ~35 MPG. Yes, that's quite efficient.
  • Planning a European road trip: You rent a car that averages 6 L/100km diesel. Gas costs €1.70 per liter. How much for a 500 km trip? (6 L/100km * 5 * €1.70 = €51). The conversion is the first step in that cost calculation.
  • Comparing two SUVs: SUV A: 22 MPG (US). SUV B: 10.5 L/100km. Which is more efficient? Convert 22 MPG to L/100km = ~10.7 L/100km. So SUV B (10.5 L/100km) is slightly more efficient.

Important Notes on Accuracy and Assumptions

The conversions use standard mathematical constants:
• 1 US gallon = 3.78541 liters
• 1 UK gallon = 4.54609 liters
• 1 mile = 1.609344 kilometers

These are the official definitions. The results are mathematically precise for the numbers you enter.

Real-world mileage varies. The converted number is the equivalent rating. Your actual fuel consumption will depend on driving style, traffic, weather, and vehicle condition. This tool is for comparing rated values, not predicting exact real-world fuel use.

Final Advice

Bookmark this page on your phone. When you're car shopping online, reading international reviews, or filling up a rental car in another country, you can pull it up in seconds. It turns a confusing jumble of units into clear, comparable numbers.

Remember: High MPG is good. Low L/100km is good. Let the calculator worry about the math in between.

FAQs About the Fuel Economy Calculator

What's the difference between US MPG and UK MPG?

The gallon size! A US gallon is 3.785 liters. A UK (Imperial) gallon is 4.546 liters. So, if a car uses the same amount of fuel to go the same distance, its MPG number in the UK will be about 20% higher than its MPG number in the US, simply because the gallon is bigger. Always check which gallon is being used.

Why do most countries use L/100km instead of MPG?

L/100km is a metric unit and relates directly to fuel consumption over a fixed, useful distance (100 km). It makes it linear and easier to calculate trip fuel costs: (L/100km value / 100) * distance in km * fuel price per liter. Also, most of the world uses the metric system, so it fits seamlessly.

How do I calculate my actual fuel economy?

This tool converts ratings. To calculate your actual economy: 1) Fill your tank completely and reset your trip meter. 2) Drive normally until you need fuel again. 3) Note the liters (or gallons) it takes to fill up and the distance (km or miles) on the trip meter. 4) Use the formula: For L/100km: (Liters / Distance in km) * 100. For MPG: Distance in miles / Gallons used. Then you can use this tool to convert your result to other units.

Is a higher km/L number always better?

Yes! Kilometers per liter (km/L) is a "bigger is better" metric, just like MPG. More kilometers you can travel on one liter of fuel means better efficiency. It's simply the inverse of L/100km (km/L ≈ 100 / L/100km).

What is considered "good" fuel economy?

It depends heavily on the vehicle type.
• Small Car: Good = < 6 L/100km (> 39 US MPG)
• Midsize Sedan/SUV: Good = 7-9 L/100km (27-33 US MPG)
• Full-size Truck/SUV: Good = 10-13 L/100km (18-23 US MPG)
Electric vehicles, of course, use a different metric altogether (kWh/100km).

Does the tool work for diesel, electric, or hybrid vehicles?

For diesel and hybrid vehicles, yes. The units are the same (MPG or L/100km), whether the energy comes from gasoline, diesel, or a combination. For fully electric vehicles (EVs), no. EVs use energy consumption units like kWh/100km or miles per kWh, which measure electricity use, not liquid fuel. That's a different type of conversion.