Fuel Consumption Calculator

US MPG and UK MPG differ because they use different gallon measurements. A US gallon is approximately 3.785 liters, while a UK (imperial) gallon is 4.546 liters. This means that the same vehicle will have a higher MPG rating when measured in UK gallons compared to US gallons. The formula to convert between them is: UK MPG = US MPG × 1.201. This difference is important to consider when comparing fuel efficiency figures from different countries.

Different regions adopted different fuel consumption metrics based on historical and practical factors. The United States has historically used MPG, which indicates how far you can go on a given amount of fuel. Many European and other countries use L/100km, which measures how much fuel is needed to travel a fixed distance. L/100km has the advantage of being directly proportional to fuel consumed (and thus to both cost and emissions), while MPG has the advantage of being intuitive for many drivers (higher is better). Different countries simply standardized on different approaches.

The mathematical conversions between fuel consumption units are precisely defined and accurate. However, real-world fuel consumption varies based on driving conditions, vehicle maintenance, weather, and driving style. The conversions provided by this calculator are mathematically exact, but remember that the original fuel consumption figures (whether MPG, L/100km, or km/L) are typically average values under standardized testing conditions and may differ from what you actually experience.

This difference comes from what each unit measures. MPG (miles per gallon) and km/L (kilometers per liter) measure distance traveled per unit of fuel—so higher numbers mean you can go further on the same amount of fuel, which is more efficient. L/100km (liters per 100 kilometers) measures fuel consumed per fixed distance—so lower numbers mean you use less fuel to travel the same distance, which is more efficient. It's two different ways of expressing the same concept, just inverted mathematically (they're reciprocal measurements).

To calculate your actual fuel consumption: (1) For MPG: Fill your tank completely, reset your trip odometer. When you need to refill, note how many miles driven and how many gallons it takes to fill the tank again. Divide miles driven by gallons used. (2) For L/100km: Same procedure, but divide liters used by kilometers driven, then multiply by 100. (3) For km/L: Divide kilometers driven by liters used. For most accurate results, use the same filling station and pump, fill to the same level, and maintain similar driving conditions between measurements.

Official fuel consumption figures are measured under standardized laboratory conditions to allow fair comparisons between vehicles. Real-world driving involves variables like traffic, weather, road conditions, driving style, vehicle load, and maintenance that affect actual consumption. Most drivers experience 10-30% higher consumption than official figures suggest. Newer testing protocols like WLTP (Worldwide Harmonized Light Vehicles Test Procedure) aim to be more realistic than older ones like NEDC (New European Driving Cycle), but a gap still exists between test results and real-world performance.

Fuel consumption directly correlates with CO₂ emissions. When fuel is burned, a predictable amount of carbon dioxide is released based on the carbon content of the fuel. For gasoline (petrol), each liter burned produces approximately 2.3 kg of CO₂. For diesel, it's about 2.7 kg of CO₂ per liter. This means that if you know a vehicle's fuel consumption rate, you can calculate its CO₂ emissions. For example, a vehicle consuming 10 L/100km of gasoline would emit about 230 grams of CO₂ per kilometer driven (10 × 2.3 ÷ 100 = 0.23 kg/km).

L/100km (liters per 100 kilometers) is the most widely used fuel consumption unit globally, being the standard in Europe, Australia, New Zealand, and most of Asia and South America. MPG (miles per gallon) is primarily used in the United States and, with imperial gallons, in the United Kingdom, though the UK is increasingly adopting L/100km. Kilometers per liter (km/L) is common in Japan, India, and several other Asian countries. The trend is toward L/100km as a global standard because it directly correlates with fuel used, costs, and emissions.