Fuel Economy Converter

About this Fuel Economy Converter

The Fuel Economy Converter translates between common distance-per-fuel and fuel-per-distance formats. Because L/100 km is an inverse measure, it requires a reciprocal conversion rather than a simple multiplication factor.

Fuel economy is measured in fundamentally opposite directions depending on the region: miles per gallon (MPG) is a bigger-number-is-better measure of distance per unit of fuel, while liters per 100 km is a smaller-number-is-better measure of fuel per unit of distance, which makes direct comparison confusing without conversion.

For related tasks, try Fuel Average Calculator, Speed Converter or Pace Converter.

How the calculation works

The tool converts each input through liters per 100 kilometers. US and imperial gallons use different volumes, so their MPG values are not interchangeable.

How to use it

1. Enter a fuel-economy value.
2. Choose the source and target units.
3. Convert to compare the equivalent efficiency.

Practical example

About 30 US MPG is approximately 7.84 L/100 km.

A car rated at 30 MPG (US) converts to approximately 7.84 liters per 100 kilometers, a conversion commonly needed by anyone comparing a US-market car's fuel economy against a European or Asian-market rating.

Things to double-check

Because MPG and L/100km move in opposite directions, converting between them is not a simple linear multiplication; always let a dedicated converter handle it rather than approximating by hand.

Four ways to say the same thing

Fuel economy can be stated as distance per volume of fuel, such as miles per gallon and kilometres per litre, or as fuel per distance, such as litres per 100 kilometres. A car that does 30 US miles per gallon uses about 7.84 litres per 100 km. The conversion between miles per gallon and litres per 100 km uses a constant of about 235.2 for US gallons and about 282.5 for imperial gallons, because the two scales run in opposite directions. In km per litre, divide 100 by the figure to get litres per 100 km: 15 km/L is 6.67 L/100 km.

US and imperial gallons

A US gallon is about 3.785 litres and an imperial gallon is about 4.546 litres, so the same car has a higher figure in imperial MPG. A car rated 30 US MPG is about 36 imperial MPG. This matters when you read reviews from different countries. Check which gallon is used before you compare, and use L/100 km or km/L if you want to avoid the confusion.

What it costs to drive

Fuel per distance makes costs easy to calculate. If fuel costs 2 per litre, a car using 8 L/100 km spends 16 for every 100 km, while one using 6 L/100 km spends 12. Over 15,000 km a year, that 2 litre difference per 100 km saves 300 litres, or 600 in fuel at that price. Use this to compare cars when you buy and to see whether paying more for an efficient model makes sense.

Real-world consumption

Quoted figures come from standard tests and real use is usually higher. Short trips, cold starts, heavy loads, roof racks, air conditioning, aggressive driving and under-inflated tyres all raise consumption, and motorway speeds above about 110 km/h cost noticeably more fuel. Track your own number by filling the tank, resetting the trip metre and dividing the fuel added by the distance driven at the next fill. Compare that with the converted rating to see how your driving differs.

Planning a road trip

Use L/100 km to estimate fuel for a journey. A 600 km trip at 7.5 L/100 km needs 45 litres. At a fuel price of 2.20 per litre, that costs about 99. The same car is rated about 31.4 US miles per gallon, because 235.2 divided by 7.5 is 31.4. Add a margin of 10 to 15 percent for traffic, a loaded car, air conditioning and hills. When you compare two cars for a long trip, use fuel per distance, since the difference between them in litres is what you pay for.

Worked example: ranking three cars

Car A is rated at 6.2 litres per 100 kilometres, car B at 32 US miles per gallon and car C at 15 kilometres per litre. Converting everything to litres per 100 km: car A stays 6.2, car B is 235.2 divided by 32, which is 7.35, and car C is 100 divided by 15, which is 6.67. So the order from most to least efficient is A, C and B. In US miles per gallon, car A is 235.2 divided by 6.2, or 37.9. Converting all ratings to one unit is the only fair way to compare, because the scales run in opposite directions.

What the difference costs per year

Suppose you drive 15,000 kilometres a year and fuel costs 1.50 per litre. Car A uses 930 litres and costs 1,395. Car C uses 1,000 litres and costs 1,500. Car B uses about 1,103 litres and costs about 1,654. The most efficient car saves about 259 a year over the least efficient one, which is over 1,300 across five years. Add the difference in purchase price, insurance and servicing to see whether a more efficient car pays for itself. If you drive very little, efficiency matters less than the purchase price.

Why real-world economy differs

Test figures are measured under standard conditions and real driving is usually worse. Air resistance rises with the square of speed, so driving at 120 kilometres per hour uses noticeably more fuel than at 100. Short trips with a cold engine, heavy loads, roof boxes, air conditioning, low tyre pressure, aggressive acceleration and cold weather all increase consumption. Keeping tyres at the recommended pressure, removing unused roof racks, combining trips and driving smoothly can reduce fuel use by several percent. Record your own figure by filling the tank, noting the distance and dividing the litres used by the distance.

Electric and hybrid vehicles

Electric cars use kilowatt-hours per 100 kilometres instead of litres. To compare with petrol cars, regulators use miles per gallon equivalent, where 33.7 kilowatt-hours is treated as the energy in a gallon of petrol. A car that uses 17 kilowatt-hours per 100 kilometres, about 27.4 per 100 miles, is rated about 123 miles per gallon equivalent. This compares energy, not cost, so check the price of electricity against fuel. Charging losses add around 10 to 15 percent to the energy drawn from the wall, so real consumption is slightly higher than the figure on the dashboard.

Key terms explained

Miles per gallon measures the distance a vehicle travels on one gallon, and the value differs for the US and imperial gallon. Kilometres per litre does the same in metric units. Litres per 100 kilometres measures how much fuel is used for a fixed distance, so lower is better. Combined economy averages city and highway figures. Real-world economy is the figure you actually achieve. Miles per gallon equivalent compares electric vehicles with petrol cars, and the drag coefficient describes air resistance.

Rules of thumb and quick checks

To convert between litres per 100 km and US miles per gallon, divide 235.2 by the other number. For imperial miles per gallon use 282.5. To change kilometres per litre to litres per 100 km, divide 100 by the figure. A rating of 8 litres per 100 km is about 29.4 US miles per gallon and 12.5 kilometres per litre. Add 10 to 20 percent to the official consumption when you estimate real costs.

Frequently asked questions