Gas Mileage Conversion Calculator: MPG to L/100km

This gas mileage conversion calculator converts fuel economy figures between miles per gallon (MPG, both US and imperial), liters per 100 kilometers (L/100km), and kilometers per liter (km/L). You enter a fuel economy value and select the unit you have; the calculator returns the equivalent values in the other common units, so you can compare vehicles or trip data across different measurement systems.

Formula

The conversion relies on fixed relationships between the units. The key constants are:

• 1 US gallon = 3.785411784 liters
• 1 imperial gallon = 4.54609 liters
• 1 mile = 1.609344 kilometers

From those, the conversion factors are derived:

• US MPG to L/100km: L/100km = 235.215 ÷ MPG (US). The constant comes from (100 km × 3.785411784 L/gal) ÷ 1.609344 km/mile.
• Imperial MPG to L/100km: L/100km = 282.481 ÷ MPG (imperial). The constant is (100 km × 4.54609 L/gal) ÷ 1.609344 km/mile.
• MPG (US) to km/L: km/L = MPG × 0.425144 (since 1 mile per US gallon = 1.609344 km ÷ 3.785411784 L).
• MPG (imperial) to km/L: km/L = MPG × 0.354006 (since 1 mile per imperial gallon = 1.609344 km ÷ 4.54609 L).
• L/100km to km/L: km/L = 100 ÷ L/100km (they are reciprocals).

All conversions are exact linear or reciprocal relationships; no rounding is applied until the final display.

Worked Example

Suppose you have a car that gets 30 US MPG and you want to know its fuel consumption in L/100km and km/L.

1. Start with the value: v = 30, from = US MPG.
2. Convert to L/100km: 235.215 ÷ 30 = 7.8405 L/100km.
3. Convert to km/L: 30 × 0.425144 = 12.7543 km/L.
4. Convert to imperial MPG (if needed): 30 × 0.832674 = 24.98 mpg (imperial).

The calculator shows: US MPG = 30.00, Imperial MPG = 24.98, L/100km = 7.84, km/L = 12.75. The result matches the formula exactly.

Why Unit Conversions Matter

Fuel economy is expressed differently around the world. The United States uses miles per gallon (US), the United Kingdom and Canada often use imperial gallons (which are about 20% larger than US gallons), and most of Europe, Asia, and Australia use liters per 100 kilometers. When comparing vehicles from different markets, reading a review from another country, or calculating trip costs using international rental cars, you need to convert between these systems. A common mistake is treating US and imperial gallons as the same; a 30 MPG (US) car would show about 36 MPG (imperial) even though it burns the same fuel.

How to Use the Calculator

Using the calculator is straightforward:

1. Enter the numeric fuel economy value in the first field.
2. Select the unit of that value from the drop-down (US MPG, Imperial MPG, L/100km, or km/L).
3. Read the results: the first output shows the equivalent US MPG, followed by imperial MPG, L/100km, and km/L.

For example, if you enter 7.5 L/100km, the calculator returns 31.36 US MPG, 37.66 imperial MPG, and 13.33 km/L. That tells you the car uses about 7.5 liters of fuel to travel 100 kilometers, which is roughly 31 miles per US gallon.

Common Mistakes and Misconceptions

• Mixing up US and imperial gallons: Always check whether the MPG figure is US or imperial. A US gallon is 3.785 L, an imperial gallon is 4.546 L. Using the wrong constant changes the result by about 20%.
• Confusing L/100km with km/L: L/100km is a consumption figure (lower is better), while km/L is an efficiency figure (higher is better). They are reciprocals, but only when using the same distance unit. 100 km/L = 1 L/100km, not 1 km/L.
• Rounding too early: If you round the conversion factor (e.g., using 235 instead of 235.215), you introduce small errors that can matter when comparing closely matched vehicles.
• Assuming MPG and L/100km are linearly related: They are not. A change from 20 to 25 MPG is a 20% improvement, but the corresponding L/100km drop is from 11.76 to 9.41 (a 20% drop as well, but the numbers are not proportional in the same way). Always convert using the reciprocal formula.

Limits of the Conversion

This calculator converts units only; it does not estimate real-world fuel economy. Actual fuel consumption depends on driving conditions, vehicle maintenance, tire pressure, load, traffic, and driving style. The conversion factors are exact, but the input value must be measured correctly. For example, if you calculate your car’s fuel economy by dividing miles driven by gallons used, make sure you fill the tank consistently and use the same measurement system throughout. Also, note that the imperial gallon is used in the UK, Canada, and some Caribbean countries, but not in the US; if you are comparing a Canadian car’s window sticker (which often shows both L/100km and imperial MPG) to a US sticker, use the correct base unit.

Frequently Asked Questions

How do I convert MPG to L/100km?

Divide 235.215 by the MPG value (if it is US MPG). For example, 35 MPG (US) = 235.215 ÷ 35 = 6.72 L/100km. If you have imperial MPG, divide 282.481 by that value instead.

What is the difference between US and imperial gallons?

A US gallon is 3.785 liters; an imperial gallon is 4.546 liters. That makes an imperial gallon about 20% larger. So a car that gets 30 MPG (US) would get about 36 MPG (imperial) on the same trip, because it travels the same miles on a larger gallon of fuel.

Why do some countries use L/100km and others use MPG?

It is largely a matter of historical convention and regulatory standards. The US and UK have traditionally used miles and gallons, while most other countries adopted the metric system. L/100km is a measure of fuel consumption (how much fuel to travel a fixed distance), while MPG is a measure of fuel economy (how far you can go on a fixed amount of fuel). Both are valid, but they are inversely related.

Is a higher MPG always better?

Yes, higher MPG means the car travels more miles per gallon, so it uses less fuel for the same distance. Similarly, lower L/100km is better because it means fewer liters to cover 100 kilometers. When comparing vehicles, use the same unit for both.

Can I convert km/L to MPG directly?

Yes. To convert km/L to US MPG, multiply by 2.35215 (since 1 km/L = 2.35215 US MPG). To convert to imperial MPG, multiply by 2.82481. For example, 15 km/L = 15 × 2.35215 = 35.28 US MPG.

Why does the calculator show both MPG and L/100km?

Because different audiences use different units. Showing all four common units lets you compare a European car’s L/100km rating to a US car’s MPG rating without doing manual math. It also helps when reading international reviews or planning trips abroad.

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in v | Fuel economy value | - | 30 | 0
sel from | Convert from | US MPG=1, Imperial MPG=2, L/100km=3, km/L=4
out us_mpg | US MPG | mpg (US) | if(from==1, v, if(from==2, v*1.20095, if(from==3, 235.215/v, v*2.35215))) | 2
out imp_mpg | Imperial MPG | mpg (UK) | if(from==1, v*0.832674, if(from==2, v, if(from==3, 282.481/v, v*2.82481))) | 2
out l100 | L/100km | L/100km | if(from==1, 235.215/v, if(from==2, 282.481/v, if(from==3, v, 100/v))) | 2
out kml | km/L | km/L | if(from==1, v*0.425144, if(from==2, v*0.354006, if(from==3, 100/v, v))) | 2