Fuel Cost Calculator – Gas Cost for a Trip
Work out how much fuel a trip will use and what it will cost. Works with miles or kilometres, MPG or L/100 km, and splits the cost between passengers.
Fuel cost = distance ÷ fuel economy × fuel price. For a 300-mile trip in a car that does 30 MPG with gas at $3.50 a gallon: 300 ÷ 30 = 10 gallons, and 10 × $3.50 = $35.
How to use Fuel Cost Calculator
- Enter the trip distance and choose miles or kilometres.
- Enter your car’s fuel economy and pick the unit (MPG US, MPG UK, L/100 km or km/L).
- Enter the fuel price per gallon or per litre.
- Tick “Round trip” to double the distance and enter how many people share the cost.
- Read the total cost, fuel needed, cost per person and cost per mile or kilometre.
How the fuel cost is calculated
The calculator first turns everything into litres and kilometres, so you can mix units freely — for example a distance in kilometres with a price per gallon. It then works out the fuel needed and multiplies it by the price. The formulas are simple:
- With MPG: gallons = miles ÷ MPG, cost = gallons × price per gallon
- With L/100 km: litres = km × L/100 km ÷ 100, cost = litres × price per litre
MPG, L/100 km and km/L
| Fuel economy | Equals | Typical for |
|---|---|---|
| 25 MPG (US) | 9.4 L/100 km | Mid-size SUV |
| 30 MPG (US) | 7.8 L/100 km | Compact car |
| 40 MPG (US) | 5.9 L/100 km | Hybrid |
| 40 MPG (UK) | 7.1 L/100 km | Small car |
A US gallon is 3.785 litres and a UK (imperial) gallon is 4.546 litres, so the same car shows a higher MPG figure in the UK. Make sure you pick the right one.
Getting a realistic number
The figure on the car’s sticker is measured in lab conditions. Real-world consumption is often 10–20% higher, especially at high motorway speeds, in winter, with a roof box or a heavy load. For the most accurate estimate, use the average shown on your dashboard, or fill the tank, note the distance and divide.
Splitting the cost
Enter the number of people who share the ride and the calculator shows the cost per person. Tick “Round trip” for an out-and-back journey. Remember that tolls, parking and wear on the car are not included in the fuel cost.
Saving fuel on a trip
Steady speeds save the most: driving at 65 mph instead of 75 mph can cut fuel use by around 10–15%. Keep tyres at the right pressure, remove unused roof racks and avoid carrying heavy items you do not need.
Running an electric car? Use the Electricity Cost Calculator and add the charger as an appliance to see what a full charge costs.
You may also find these free tools useful: Compound Interest Calculator, Electricity Cost Calculator and Loan Calculator.
Frequently asked questions
How do I calculate gas cost for a trip?
Divide the distance by your car’s MPG to get gallons, then multiply by the price per gallon. The calculator does this for you and also handles litres and kilometres.
How much gas will I use for 100 miles?
Divide 100 by your MPG. A car that does 25 MPG uses 4 gallons for 100 miles; at 40 MPG it uses 2.5 gallons.
How do I convert MPG to L/100 km?
Divide 235.21 by the US MPG figure. For example, 30 MPG is 235.21 ÷ 30 = 7.8 L/100 km. For UK MPG divide 282.48 by the figure.
Should I use highway or city MPG?
Use the figure that matches most of your route. For long motorway trips the highway figure is closer; for town driving use the city figure.
Does the calculator include tolls?
No. It shows only the cost of fuel. Add tolls, parking and other costs separately.
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