How much CO2 does a litre of petrol produce?

One litre of petrol (gasoline) produces approximately 2.31 kg of CO2. One litre of diesel produces about 2.68 kg of CO2.

What is the average fuel consumption of a car?

A modern petrol car averages 6–8 L/100km (35–47 MPG). Diesel cars typically achieve 5–7 L/100km. Hybrids can reach 4–5 L/100km. SUVs and large vehicles usually consume 9–14 L/100km.

How to Calculate Fuel Cost for Any Trip

Q: How do I calculate fuel cost for a road trip?

Divide the distance by your car's fuel efficiency to get the fuel needed, then multiply by the fuel price. In metric: (km / 100) × L/100km × price per litre. In imperial: (miles / MPG) × price per gallon.

Q: How do I convert MPG to L/100km?

Divide 235.21 by the MPG value. For example, 30 MPG = 235.21 / 30 = 7.84 L/100km. To convert L/100km to MPG, divide 235.21 by the L/100km figure.

Skip the math — our free tool calculates everything instantly.

Fuel Cost Calculator — Free Online Tool

The fuel cost formula

The calculation has two steps: find how much fuel you need, then multiply by the price.

Metric (L/100km)

Fuel needed (litres) = (Distance km ÷ 100) × L/100km

Trip cost = Fuel (L) × Price per litre

Example: 300 km trip, car consumes 7.5 L/100km, fuel costs €1.68/L:

Fuel needed: (300 ÷ 100) × 7.5 = 22.5 litres
Trip cost: 22.5 × €1.68 = €37.80

Imperial (MPG)

Fuel needed (gallons) = Distance (miles) ÷ MPG

Trip cost = Fuel (gal) × Price per gallon

Example: 200-mile trip, car gets 32 MPG, gas costs $3.45/gal:

Fuel needed: 200 ÷ 32 = 6.25 gallons
Trip cost: 6.25 × $3.45 = $21.56

Round trips

For a round trip, simply double the one-way distance before calculating. A 150 km one-way journey becomes a 300 km round trip. Our calculator includes a Round trip toggle that does this automatically.

Splitting the cost between passengers

To find the cost per person, divide the total trip cost by the number of passengers. If a 400 km trip costs $48 and there are 3 people in the car, each person pays $48 ÷ 3 = $16.00. Carpooling is one of the most effective ways to cut individual fuel costs.

How to convert MPG to L/100km

The conversion formula is: L/100km = 235.21 ÷ MPG

Common conversions:

25 MPG = 9.4 L/100km (large SUV)
35 MPG = 6.7 L/100km (average family car)
50 MPG = 4.7 L/100km (hybrid)
60 MPG = 3.9 L/100km (very efficient hybrid)

To convert the other way: MPG = 235.21 ÷ L/100km

CO₂ emissions from driving

Fuel combustion releases CO₂ proportional to the volume burned. Standard values used by environmental agencies:

Petrol (gasoline): 2.31 kg CO₂ per litre
Diesel: 2.68 kg CO₂ per litre

For the 300 km metric example above (22.5 litres of petrol): 22.5 × 2.31 = 52 kg of CO₂. Over a year of typical driving (15,000 km at 7.5 L/100km), that same car emits approximately 2.6 tonnes of CO₂.

Comparing two vehicles

The fuel cost calculator includes a vehicle comparison panel. Enter the same trip details for both cars to instantly see which one costs less and by how much. This is especially useful when:

Deciding whether a more fuel-efficient car justifies its higher purchase price.
Choosing between a petrol and a diesel version of the same model.
Evaluating whether a long motorway trip is cheaper in your car or a rental.

Tips to reduce your fuel costs

Fuel efficiency is partly about the car and partly about how you drive it. Small habits add up significantly over thousands of kilometres.

Drive at steady speeds: Most cars are most efficient between 80 and 100 km/h (50–60 mph). Motorway driving above 120 km/h increases fuel use sharply due to aerodynamic drag.
Anticipate stops: Coasting to a red light instead of braking hard saves fuel. Modern fuel-injected engines use almost zero fuel when decelerating.
Keep tyres properly inflated: Under-inflated tyres increase rolling resistance. Fuel use rises by approximately 0.5% for every 10 kPa drop in tyre pressure.
Remove roof racks and boxes when not in use: A roof box increases aerodynamic drag by 10–25%, raising fuel consumption noticeably at motorway speeds.
Service your car regularly: A clogged air filter alone can increase fuel use by 10%. Fresh oil, a clean filter and properly gapped spark plugs keep efficiency up.
Use air conditioning sparingly: AC can increase fuel consumption by 5–20% in city driving. At motorway speeds, opening windows has a similar drag penalty — use AC there instead.
Carpool: Splitting a journey between two people halves your individual fuel and CO₂ footprint instantly.

Frequently asked questions

How do I calculate fuel cost for a road trip?

Use the formula: (distance ÷ 100) × L/100km × price per litre for metric, or (distance ÷ MPG) × price per gallon for imperial. Enter the values into our Fuel Cost Calculator for an instant result.

How do I convert MPG to L/100km?

Divide 235.21 by the MPG number. 30 MPG = 235.21 ÷ 30 = 7.84 L/100km. To go back, divide 235.21 by the L/100km value.

What is average fuel consumption for a car?

Petrol cars: 6–8 L/100km (35–47 MPG). Diesel: 5–7 L/100km. Hybrids: 4–5 L/100km. SUVs: 9–14 L/100km.

Conclusion

Calculating trip fuel cost takes just two steps: find the fuel needed from distance and efficiency, then multiply by the price. Once you know the formula, you can estimate costs in your head for any journey. For precise figures — especially for round trips, multiple passengers or vehicle comparisons — use the free Fuel Cost Calculator.

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