UtilibyWritten by the Utiliby editorial team · Last updated October 17, 2026 · Rules and formulas reviewed October 2026
What this free gas trip cost calculator does
Planning a road trip, a commute or a drive to see family? A gas trip cost calculator tells you how much fuel you will use and what it will cost before you leave. This free online tool works in miles or kilometres, with fuel economy in US mpg, UK mpg, litres per 100 km or km per litre, and prices per US gallon, UK gallon or litre, so it fits drivers in the US, UK, Canada, Europe and beyond.
It shows the fuel needed in litres and gallons, the fuel cost, the cost per mile or kilometre, tolls and extras, the share per person for carpools, and the CO2 emitted for petrol or diesel. A chart shows how the total changes if fuel prices move. A second tab compares the same trip and your annual driving in a petrol or diesel car with an electric car, and a third tab totals a journey with several stops. Everything runs in your browser.
How to use the gas trip cost calculator
- Enter the distance and choose miles or kilometres. Tick Round trip if you are coming back.
- Enter your fuel economy and pick its unit.
- Enter the fuel price and pick per gallon or per litre.
- Add tolls and parking, and the number of people sharing.
- Read the cost, the fuel needed and the cost per person.
- Use the other tabs to compare with an electric car or plan multiple stops.
The fuel cost formula
In US units, fuel cost equals distance divided by miles per gallon, times the price per gallon. A 250-mile trip each way is 500 miles. At 28 mpg that needs 500 / 28 = 17.86 gallons, and at $3.45 a gallon the fuel costs $61.61, or $15.40 each for four people. That is about 12.3 cents a mile. In metric units, litres equal kilometres times L/100 km divided by 100. A trip of 800 km at 7 L/100 km uses 56 litres, and at 1.65 per litre costs 92.40.
| US mpg | L/100 km | UK mpg |
|---|---|---|
| 20 | 11.8 | 24.0 |
| 28 | 8.4 | 33.6 |
| 35 | 6.7 | 42.0 |
| 50 | 4.7 | 60.0 |
mpg, L/100 km and km per litre
Fuel economy is expressed differently around the world. The United States uses miles per gallon, where more is better. Most of Europe, Canada and Australia use litres per 100 kilometres, where less is better. Some countries use kilometres per litre. A US gallon is 3.785 litres and a UK gallon is 4.546 litres, so the same car shows a bigger UK mpg figure. The calculator converts everything to litres per 100 km internally and shows your economy in US mpg, UK mpg and L/100 km together.
Gas versus electric
Running an electric car usually costs less per mile than petrol if you charge at home, but the gap depends on your electricity tariff and local fuel prices. On the 500-mile example, an electric car using 30 kWh per 100 miles needs 150 kWh. At $0.17 per kWh that is $25.50, against $61.61 for petrol. Over 12,000 miles a year the difference is about $867. Charging on public fast chargers can cost much more per kWh, so enter the price you will really pay. The tab also compares CO2, using an editable grid factor.
Sharing the cost of a trip
When friends or colleagues carpool, split the total, not just the fuel. Add tolls and parking to the extras box, enter the number of people including the driver, and the calculator gives each person's share. Some groups also add a small amount for wear and tear, which you can include as an extra. Agreeing the number before the trip avoids awkward conversations afterwards.
How to cut fuel costs on the road
- Drive smoothly. Gentle acceleration and anticipating traffic saves fuel.
- Mind your speed. Fuel use rises quickly above about 55 to 60 mph.
- Keep tyres properly inflated.
- Remove roof racks and extra weight.
- Plan the route to avoid congestion and detours.
- Compare pump prices and fill up where it is cheaper.
Carbon emissions of a trip
Burning one US gallon of petrol releases about 8.89 kg of carbon dioxide, and a gallon of diesel about 10.18 kg, according to the US Environmental Protection Agency. The 17.86 gallons in the example emit roughly 159 kg of CO2. Sharing the ride divides the footprint per person. For electric cars, emissions depend on how the electricity is generated, so the tool uses a round editable factor of 0.4 kg per kWh that you can change to match your grid.
Accuracy, privacy and responsible use
The calculator multiplies the figures you enter. Real fuel use varies with speed, load, weather, terrain and driving style, and prices change along the route. Costs exclude wear, insurance and depreciation unless you add them. Nothing you enter leaves your browser.
Related free tools
Use these free online tools together with this one:
- Work out the cost of charging at home with the electricity cost calculator.
- Divide the trip's other costs fairly with the split bill calculator.
- Compare fuel and other prices per unit with the unit price calculator.
- Add the trip to your plan with the budget planner calculator.
- Plan the flying part of a longer trip with the jet lag calculator.
Frequently asked questions
How do I calculate the cost of a gas trip?
Divide the distance by your miles per gallon to get gallons, then multiply by the price per gallon. 500 miles at 28 mpg is 17.86 gallons, and at $3.45 a gallon the fuel costs $61.61.
How do I calculate fuel cost in kilometres?
Multiply the distance in km by the fuel use in L/100 km, divide by 100 to get litres, and multiply by the price per litre. 800 km at 7 L/100 km uses 56 litres, and at 1.65 per litre costs 92.40.
How do I convert mpg to L/100 km?
Divide 235.215 by the mpg (US). 28 mpg is 8.4 L/100 km. For UK mpg, divide 282.481 by the figure.
What is the difference between US and UK mpg?
A UK gallon is 4.546 litres and a US gallon is 3.785 litres, so a UK mpg figure is about 20 percent higher for the same car. Choose the right unit for your car's figure.
What fuel economy should I use?
Use the real-world figure from your trip computer or past fill-ups. Official ratings are often optimistic, and motorway speed, load and weather change it.
How do I split gas costs between passengers?
Enter the number of people sharing and the tool divides the total, including tolls and extras, by the number of people.
Does it work for round trips?
Yes. Tick Round trip and the one-way distance is doubled.
Can I include tolls and parking?
Yes. Add them in the extras box and they are included in the total and in the per-person cost.
How much does an electric car cost per trip?
Multiply the distance by the car's kWh per mile and by your electricity price. 500 miles at 30 kWh per 100 miles is 150 kWh, which at $0.17 per kWh costs $25.50.
Is an electric car cheaper than a gas car per mile?
Often yes on home charging, but it depends on electricity and fuel prices, efficiency and whether you use public fast chargers. The second tab compares both for your trip and year.
How much CO2 does a trip produce?
Burning a US gallon of petrol emits about 8.89 kg of CO2 and a gallon of diesel about 10.18 kg, per the US EPA. The 500 mile example emits around 159 kg.
How can I reduce fuel costs on a road trip?
Drive smoothly at moderate speeds, keep tyres inflated, remove roof boxes, travel light, avoid idling, plan routes and share the ride.
Can I plan a trip with several stops?
Yes. Use the multi-stop tab to enter up to six legs and see the total distance, fuel and cost.
Does it include vehicle wear or depreciation?
No. It covers fuel, tolls and extras. Add maintenance and depreciation as extras for a fuller cost per mile.
Does speed change my fuel use?
Yes. Most cars use more fuel at higher speeds because air resistance rises sharply. Use an economy figure that matches the type of driving.
Is my data stored or sent anywhere?
No. Everything runs in your browser.
Is this gas trip cost calculator free?
Yes. It is free to use online with no sign-up.
Sources and further reading
- U.S. Environmental Protection Agency, Greenhouse gases equivalencies calculator: calculations and references.
- U.S. Department of Energy, FuelEconomy.gov.
- U.S. Energy Information Administration, Gasoline and diesel fuel update.
- U.S. Department of Energy, Alternative Fuels Data Center.
Sources were consulted in October 2026. Standards and rules can change, so always check the official page for your situation.