Miles per gallon (US) to Kilometer per liter

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.

India adopted km/L because it intuitively answers "how far can I go on one liter?" — a question that resonates strongly in a price-sensitive market where drivers often buy fuel in specific liter amounts rather than filling up. The Bureau of Energy Efficiency (BEE) publishes official star ratings in km/L.

India historically subsidised petrol and diesel prices, keeping pump costs artificially low and weakening the incentive to buy fuel-efficient cars. As subsidies have been rolled back since 2014, the BEE star rating in km/L has become a genuine purchasing factor. A one-star jump (roughly 3–4 km/L better) now translates to noticeable monthly savings, pushing buyers toward smaller engines, hybrids, and CNG vehicles.

A typical 125cc commuter motorcycle in India or Southeast Asia achieves 40–60 km/L in city riding, far exceeding any passenger car. The Honda CB Shine, one of India's best-sellers, claims about 55 km/L — a major reason two-wheelers dominate Asian commuting.

Part of it is real — Japanese kei cars are lighter and smaller. But the old JC08 test cycle was also more lenient than European WLTP, inflating numbers by 10–20%. Japan has since adopted WLTC testing, narrowing the gap and giving more realistic km/L figures.

It is achievable but only for small, lightweight cars under ideal highway conditions. In real-world mixed driving, most non-hybrid petrol cars top out around 15–17 km/L. Hitting 20 km/L consistently without hybrid assistance requires something like a sub-1000 kg car with a 1.0L engine.