Fuel Economy
Unit Converter

If you've ever tried to compare a car's fuel economy figure from a US review site against a spec sheet from a European or Japanese manufacturer, you've probably run into a wall of confusing, seemingly incompatible numbers. That's because there is no single global standard for expressing how efficiently a car burns fuel — instead, each region built its own convention around the measurement system it already uses for distance and volume.

The United States uses miles per gallon (MPG), based on the US gallon (3.785 liters), where a bigger number always means better efficiency. The United Kingdom historically used the same style of measurement but with the imperial gallon (4.546 liters), which is roughly 20% larger than the US gallon — so a UK MPG figure and a US MPG figure for the exact same car will never match, even though nothing about the car's actual fuel consumption has changed. This trips up a lot of people importing cars or comparing spec sheets between US and UK sources.

Most of the rest of the world — continental Europe, Australia, South Africa, and much of Africa and Latin America — uses the metric system and expresses fuel economy as liters consumed per 100 kilometers (L/100km). This flips the logic: instead of measuring how far you get per unit of fuel, it measures how much fuel you burn over a fixed distance, which means a lower number is better. Meanwhile, kilometers per liter (km/L) is common in Japan, parts of Southeast Asia, and increasingly in Nigeria and other African markets, and it works the same direction as MPG — bigger is better — just using metric units instead of miles and gallons.

This is exactly the kind of problem a converter solves cleanly without needing any make, model, or country-specific data — it's pure unit math, the same everywhere in the world, which is why the tool above works identically whether you're comparing a Lagos-market Toyota to a US EPA rating or a UK dealer listing to a Japanese import spec sheet.

These are the exact formulas the calculator above uses, derived from the fact that 1 US gallon = 3.785411784 liters, 1 UK gallon = 4.54609 liters, and 1 mile = 1.609344 kilometers:

The 235.21 and 282.48 constants come from converting gallons and miles into liters and kilometers, then normalizing to a 100km base distance. You don't need to memorize any of this — the tool above does it live as you type — but it's useful to understand why the numbers move the way they do, and why doubling your MPG doesn't simply halve your L/100km in a way that's intuitive at a glance (it does, in fact, work out that way, but the relationship is inverse rather than linear, which is why a small MPG change at the high end matters less than the same change at the low end).

If you're comparing a used import listing that quotes UK MPG against a Japanese auction sheet quoting km/L, or you're trying to work out what a US EPA sticker actually means for your monthly fuel budget in a country that fuels in liters, getting the conversion right isn't just academic — it directly affects how much you'll actually spend at the pump. A car advertised at "40 MPG" sounds efficient until you realize the listing is quoting UK MPG rather than US MPG, which converts to a noticeably different real-world liters-per-100km figure.

It also matters when you're cross-shopping between markets — comparing a Nigerian-market Toyota Corolla spec sheet (often in km/L) against a European brochure (in L/100km) against an American review (in MPG) requires converting all three into the same unit before the comparison means anything. Running the numbers through a converter first means you're comparing like with like, rather than assuming a bigger number is automatically better without checking which direction that particular unit runs.

A converted number on its own is only half the picture — the real value comes from turning it into money. Once you know a car's consumption in L/100km, the arithmetic for a monthly fuel budget is simple: multiply your expected monthly distance in kilometers by the L/100km figure, divide by 100, and multiply by the local fuel price per liter. A car doing 8 L/100km driven 1,200km a month at a fuel price of ₦1,200/liter, for example, burns roughly 96 liters and costs about ₦115,200 for that month, before accounting for traffic, air conditioning use, or a heavy right foot, all of which push real-world consumption above the manufacturer's tested figure.

This is also where unit confusion gets expensive in practice, not just on paper. Someone comparing a "35 MPG" American listing against a "15 km/L" Japanese-market alternative has no intuitive way to tell which is actually cheaper to run without converting both into the same unit first — and the difference between US and UK MPG alone is large enough to change which car looks like the better deal. If you're budgeting for a car purchase, especially an import, it's worth running every spec sheet you're comparing through a converter like the one above before you commit, rather than trusting whichever number looks the biggest.

For a fuller cost picture that includes actual local fuel prices rather than just the physics of conversion, pair this tool with our Fuel Cost Calculator, which takes a consumption figure and turns it into a real naira-and-kobo running cost based on distance and current pump prices.