Fuel cost of a trip from distance, mpg or L/100 km and fuel price, with tolls, a round-trip option and the cost split per person.
By AdminDrafted with AI writing toolsUpdated Checked examples: 4
300 km at 7 L/100 km burns 21 L of fuel costing $36.75; with $10.00 in tolls and parking the trip costs $46.75, or $23.38 each for 2 people.
Economy converted to km/L (7 L/100 km).
Fuel used is the distance divided by the fuel economy, and fuel cost is that volume times the price per litre or gallon. Tolls and parking are added for each leg, a round trip doubles both the distance and the tolls, and the total is divided by the people sharing the car. Economy can be entered in L/100 km, km/L, US mpg or UK mpg, and the price per litre, US gallon or imperial gallon.
With the defaults, 300 km at 7 L/100 km burns 21 L. At 1.75 a litre that is 36.75 of fuel, and 10 of tolls brings the trip to 46.75, or 23.38 each for two people. The same sum prices a commute, a holiday drive or a share of the petrol money.
The answer is only as good as the economy figure. Speed, traffic, load and cold weather all change consumption, so a figure worked out from your own fill-ups gives a closer cost than the official rating.
Work out the fuel used, then multiply by the price. Fuel used is distance × L/100 km ÷ 100, or miles ÷ mpg. A 300 km drive at 7 L/100 km uses 21 L; at 1.75 a liter that is 36.75 of fuel, and 10 of tolls makes 46.75, or 23.38 each for two people.
For a round trip, double both the distance and the tolls. Add parking and other trip costs before dividing among the people sharing the car.
US gallons. 500 miles each way at 30 mpg is 1,000 miles ÷ 30 = 33.33 gallons. At $3.50 a gallon that is $116.67, or $29.17 each for four people.
UK mpg with fuel priced per liter. 200 miles at 45 UK mpg uses 200 ÷ 45 = 4.444 imperial gallons, or 4.444 × 4.54609 = 20.20 L. At £1.45 a liter the fuel costs £29.30.
The UK example mixes units on purpose: British cars are rated in miles per imperial gallon while pumps charge per liter. Convert the fuel volume to the unit of the price before multiplying.
Default is the 300 km drive above, and US round trip is the 500-mile example for four people. UK economy is the 200-mile drive at 45 UK mpg and £1.45 a liter, for one person.
Tolls each way is 100 km one way at 5 L/100 km and 2 a liter, with 5 in tolls each way, driven both ways and split three ways. Imperial fuel price is 100 miles at 40 UK mpg with fuel at 6 per imperial gallon.
| Scenario | Fuel used, L | Trip total | Per person |
|---|---|---|---|
| Default | 21.000000 | 46.750000 | 23.375000 |
| US round trip | 126.180393 | 116.666667 | 29.166667 |
| UK economy | 20.204844 | 29.297024 | 29.297024 |
| Tolls each way | 10.000000 | 30.000000 | 10.000000 |
| Imperial fuel price | 11.365225 | 15.000000 | 15.000000 |
In the tolls row, 200 km at 5 L/100 km is 10 L, or 20 of fuel, and the two 5 tolls bring it to 30: 10 each.
Divide the whole trip cost, fuel plus tolls and parking, by the number of people sharing it, including the driver if they share. Shares rounded to the cent may not add back exactly: two shares of 23.38 make 46.76 for a 46.75 trip.
Per-kilometer and per-mile costs include the tolls. The default trip costs 0.1558 per km in total but 0.1225 per km for fuel alone, because the fixed 10 of tolls is spread over 300 km.
This is the out-of-pocket cost of the drive. Wear, insurance and depreciation are extra; the car ownership cost calculator adds them up.
The US Department of Energy's driving-efficiency guidance says aggressive driving can lower gas mileage by roughly 15–30% at highway speeds and 10–40% in stop-and-go traffic. Load and weather move it too.
For the closest estimate, use economy measured from your own fill-ups, which the gas mileage calculator works out from odometer readings and fuel added.
For an electric car, the EV charging calculator prices a charge and compares it with petrol; the fuel economy converter handles mpg and L/100 km on their own.
Checked against: Hand calculation: 300 × 7/100 = 21 L × 1.75 = 36.75 + 10 = 46.75; ÷ 2 = 23.375
Checked against: Hand calculation: 1,000 mi ÷ 30 mpg = 33.33 gal × 3.50 = 116.67; ÷ 4 = 29.17
Checked against: 200 ÷ 45 × 4.54609 L = 20.2048 L × 1.45 = 29.297
Checked against: Hand calculation: 200 km × 5/100 = 10 L × 2 = 20, plus 2 × 5 tolls = 30; ÷ 3 = 10
Divide the distance by the fuel economy to get the fuel used, then multiply by the price. 300 km at 7 L/100 km uses 300 × 7 ÷ 100 = 21 L, which costs 36.75 at 1.75 a litre. In US units, 500 miles at 30 mpg uses 16.7 gallons, or $58.33 at $3.50 a gallon. Add tolls and parking, then double everything for a round trip.
Divide 235.21 by US mpg, or 282.48 by UK mpg; the same division converts L/100 km back to mpg. The constants follow from the US gallon (231 cubic inches, 3.785411784 L), the imperial gallon (4.54609 L) and the mile (1.609344 km), as listed in NIST SP 811. So 7 L/100 km is 33.6 US mpg or 40.4 UK mpg.
The imperial gallon holds 4.54609 L and the US gallon 3.785 L, so a UK gallon is 20% larger and the same car travels 20% further on it. Multiply UK mpg by 0.8327 to get US mpg: 45 UK mpg is 37.5 US mpg. Reading a UK figure as US mpg understates the fuel used by a sixth.
Add fuel, tolls and parking and divide by the number of people sharing: the default 46.75 trip is 23.38 each for two. That covers only out-of-pocket costs. To include wear, insurance and depreciation, some drivers charge the IRS standard mileage rate instead, 76 cents a mile for business driving from 1 July 2026 (IR-2026-29); fuel alone at 30 mpg and $3.50 a gallon is 11.7 cents a mile.
Driving style and weather move real consumption away from the label. The US Department of Energy's fueleconomy.gov says aggressive driving can cut gas mileage by 15–30% at highway speeds and 10–40% in stop-and-go traffic, and a petrol car's city mileage is roughly 15% lower at 20 °F (−7 °C) than at 77 °F (25 °C). Economy measured from your own fill-ups gives the closest trip cost.
This calculator includes 4 worked examples with independently sourced answers. They run in the test suite, and you can run them here too.