Fuel Consumption Calculator

Fuel consumption formulas

Fuel consumption describes how much fuel a vehicle uses to cover a distance. It is quoted in two opposite ways: as fuel per distance (litres per 100 km, common in Europe, Canada and Australia) or as distance per fuel (miles per gallon in the US, kilometres per litre in parts of Asia and South America). A lower number is better in the first style and a higher number is better in the second.

L/100 km = fuel (L) ÷ distance (km) × 100

km/L = distance (km) ÷ fuel (L)

mpg = distance (miles) ÷ fuel (gallons)

When you enter a price, the calculator also gives the running cost in two forms: the cost of each mile or kilometre, and how far one dollar of fuel takes you.

cost per distance = price × fuel ÷ distance

distance per dollar = distance ÷ (price × fuel)

How to measure your own consumption

1. Fill the tank completely and note the odometer, or reset the trip meter to zero.
2. Drive as usual until the tank is at least half empty. A longer stretch smooths out the error from filling.
3. Fill up again to the same level (for example, the first automatic click of the pump) and write down the fuel added.
4. Enter the distance on the trip meter as Distance travelled and the fuel added as Fuel spent.

Example 1 (metric). A driver covers 612 km and needs 41.8 litres to refill. Consumption is 41.8 ÷ 612 × 100 = 6.83 L/100 km, which is 612 ÷ 41.8 = 14.64 km per litre. At 1.72 per litre the fill-up cost 71.90, or about 0.12 per km (8.51 km for each unit of currency spent).

Example 2 (US units). 300 miles on 10 gallons is 300 ÷ 10 = 30 mpg. With gas at $3.50 the cost per mile is 3.50 × 10 ÷ 300 = $0.1167, shown as $0.12 per mile, and each dollar buys 300 ÷ 35 = 8.57 miles.

Results show two decimals, so a cost per distance that is below half a cent displays as $0. In that case look at the 'per $' figure instead.

Different ways to express fuel economy

To compare a car rated in one style with another rated in a different style, convert them to a common unit. The table uses the US gallon (3.785 litres). The imperial gallon used in the UK is larger (4.546 litres), so the same car has a higher miles-per-gallon figure there, about 1.2 times as high.

The relationship is inverse: L/100 km = 235.21 ÷ mpg (US). That is why going from 15 to 20 mpg saves far more fuel per mile than going from 40 to 45 mpg, even though both are an improvement of a few mpg. For any other value, use the fuel consumption converter, and for a trip budget use the fuel calculator.

If you only want the miles-per-gallon figure from an odometer reading, the MPG calculator takes the current and previous readings instead of the distance.

How to achieve better fuel efficiency

Fuel use is the result of the vehicle, the road and the driver. Small habits add up:

• Smooth driving. Gentle acceleration, early lifting off the throttle and fewer hard stops can improve economy noticeably, especially in town.
• Speed. Air resistance rises with the square of speed, so a steady 100 km/h is much cheaper than 130 km/h.
• Tyres and alignment. Keep tyres at the recommended pressure and check alignment if the car pulls to one side.
• Weight and drag. Take out heavy items and remove roof racks and boxes when not in use.
• Engine care. Regular servicing, the right oil grade and a clean air filter keep the engine efficient.
• Fewer cold starts. Short trips with a cold engine use the most fuel per kilometre. Combine errands where you can.

Track your consumption over several tanks. One fill-up can be misleading because pump cut-off varies, but the average of five or six gives a trustworthy baseline, and any sudden change is an early hint of a problem such as a dragging brake or low tyre pressure.