Miles per gallon (US) to Liters per km

The EPA tests cars on a dynamometer in a lab, not on real roads. While EPA adjusted its formulas in 2008 to be more realistic, factors like cold weather, air conditioning, aggressive driving, hilly terrain, and short trips still cause most drivers to underperform the sticker by 10–20%.

The US never adopted the metric system for everyday use, and mpg has been embedded in American car culture since the 1970s oil crisis when fuel economy became a selling point. CAFE standards codified mpg into federal law, making a switch politically and practically difficult.

The mpg illusion is the cognitive bias where people assume equal mpg improvements save equal fuel. In reality, upgrading a truck from 12 to 14 mpg saves more gallons over 10,000 miles than upgrading a sedan from 30 to 50 mpg. This is because mpg is a reciprocal measure — savings are concentrated at the low end.

Multiply US mpg by 1.201 to get UK mpg (because the imperial gallon is 20.1% larger than the US gallon). A car rated 30 US mpg is about 36 UK mpg. Many Americans visiting the UK are confused when British cars seem to get impossibly high mpg numbers.

The 2025 Hyundai Ioniq Blue held the record for non-plug-in cars at 59 mpg combined. Among hybrids, the Toyota Prius has consistently led, reaching 57 mpg combined in recent model years. Plug-in hybrids running on electricity achieve MPGe ratings over 100, but that is a different metric entirely.

L/km is the raw mathematical unit that telematics systems and engine control units log internally. It maps directly to instantaneous fuel flow divided by speed, making it ideal for real-time calculations. Multiplying by 100 to get L/100km is a display convenience for humans, not a computing necessity.

Modern telematics units sample fuel flow and GPS speed several times per second, computing instantaneous L/km continuously. When the value spikes — hard acceleration, excessive idling, speeding — the system triggers an in-cab alert or scores the behavior for later review. Over thousands of vehicles, coaching drivers to shave even 0.005 L/km off their average can save a fleet millions of liters per year.

An F1 car burns roughly 0.35–0.45 L/km under race conditions, about five times more than a typical passenger car. FIA regulations cap total fuel at 110 kg per race, forcing teams to balance speed against consumption strategically.

Yes, 0.05 L/km (equivalent to 5 L/100km or ~47 US mpg) is quite efficient. Most petrol hybrids achieve this range. A non-hybrid petrol car would need to be a well-optimized compact to hit that mark consistently in mixed driving.

OBD-II standardized on raw per-kilometer (or per-mile) metrics because the ECU calculates consumption at the granular level. Your dashboard or app multiplies by 100 for display. The raw L/km reading updates in real time and is more useful for diagnosing injector performance or driving behavior.