Fuel Economy Converters

Fuel Economy: Making Sense of American Car Reviews

You're reading a review of the Toyota RAV4 on an American car site. It says the car gets "30 mpg combined." Sounds decent, but what does that actually mean for you at the bowser in Sydney? That's 7.8 L/100km. Now you've got a number you can compare against the sticker on the dealer's window.

This is the most common reason Australians need fuel economy conversions. We don't import many US cars (wrong side of the road), but we read plenty of American reviews. MotorTrend, Car and Driver, Edmunds. They all report in miles per gallon. Every Australian car buyer compares specs online before walking into a dealer, and half the best reviews are written in MPG.

Australia measures fuel efficiency as litres per 100 kilometres (L/100km). Lower is better. A small hatchback like a Corolla does about 6.0 L/100km. A mid-size SUV sits around 8 to 9. A LandCruiser or large American pickup is 12 to 14. The US and UK both use miles per gallon (MPG), but with different sized gallons. A US gallon is 3.785 litres. An imperial gallon is 4.546 litres. So 30 mpg US is not the same as 30 mpg UK. This catches people out constantly.

The scales run in opposite directions, which is the core confusion. In L/100km, lower numbers mean better economy. In MPG, higher numbers mean better economy. A car doing 5 L/100km is sipping fuel. A car doing 15 L/100km is drinking it. But a car doing 47 mpg is frugal, and a car doing 16 mpg is thirsty. Your brain has to flip the scale every time you switch between the two systems.

Working out real-world fuel costs

L/100km makes fuel cost calculations dead simple. Take your L/100km figure, multiply by the fuel price, and you've got your cost per 100 km. If fuel is $1.85/L and your car does 7.5 L/100km, that's $13.88 per 100 km. Driving 15,000 km a year costs about $2,081 in fuel. Try doing that mental maths with MPG. It's doable, but it's not instant.

This is also why L/100km is a better metric for comparing cars. The difference between 5 and 6 L/100km saves you about $278 a year at current fuel prices over 15,000 km. The difference between 10 and 11 L/100km saves the same amount. With MPG, the savings are not linear: the jump from 15 to 20 mpg saves far more fuel than the jump from 35 to 40 mpg, even though both are "5 mpg better." This is called the MPG illusion, and it's a real problem with the American system.

Official figures vs reality

The combined fuel figure on a new car's sticker in Australia comes from the WLTP test cycle (Worldwide Harmonised Light Vehicle Test Procedure). It's more realistic than the old NEDC test, but still optimistic. Expect real-world consumption to be 10 to 20 percent higher than the official figure. A car rated at 6.0 L/100km will probably do 6.5 to 7.0 in mixed driving. Highway cruising is better. Stop-start city traffic is worse.

American EPA figures tend to be closer to real-world driving than the old Australian test cycle, but still optimistic. If an American review says a car gets 28 mpg combined on the EPA cycle (8.4 L/100km), expect something like 9 to 9.5 L/100km in typical Australian conditions. Traffic, hills, air conditioning in summer, and short trips all push consumption up.

Diesel, hybrid, and electric

Diesel cars typically use 20 to 30 percent less fuel than their petrol equivalents. A diesel SUV might do 6.5 L/100km where the petrol version does 8.5. But diesel costs slightly more per litre and the engines are more expensive to service. For high-kilometre drivers (over 20,000 km a year), diesel usually pays for itself. For city commuters doing 10,000 km, petrol or hybrid is often cheaper overall.

Hybrids change the game entirely. A RAV4 Hybrid does about 4.8 L/100km combined. Some plug-in hybrids can do under 2 L/100km if you charge daily and your commute is short enough. EVs don't use L/100km at all. They use kWh/100km, which is a different converter entirely (check our energy converters).