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Gas Cost Calculator

This gas cost calculator estimates how much fuel a trip uses and what it costs, one way or round trip, with tolls and parking added. Enter two vehicles' efficiency to see which is cheaper to drive.

One-way distance

Distance unitTripEfficiency unit

Vehicle 1 efficiency

Vehicle 2 efficiency

Price per litre/gallon

Tolls, parking and other total costs

Fuel prices must use the same volume unit as the selected efficiency. US and imperial gallons differ. Tolls and extras are entered for the complete trip.

Trip distance km: 100.00

Vehicle	Fuel in chosen unit	Fuel cost	Total cost
1	7.00	10.50	10.50
2	9.00	13.50	13.50

How fuel cost is calculated

Trip distanceone-way km × 2 for a round trip
Fuel in L/100kmlitres = km × L/100km ÷ 100
Fuel in mpggallons = (km ÷ 1.609344) ÷ mpg
Fuel costfuel × price per litre or gallon
Total costfuel cost + tolls, parking and other costs

Distance is always entered in kilometers; for miles, multiply by 1.609344 first. Fuel comes out in liters for L/100km and in gallons for either mpg unit. Both vehicles share the distance, price and extras, so the comparison isolates efficiency.

Fuel prices must use the same volume unit as the selected efficiency. US and imperial gallons differ. Tolls and extras are entered for the complete trip.

Worked example: a 300-mile road trip, there and back

300 miles is 482.8 km, so the round trip is 965.6 km. Gas is $3.40 a US gallon and tolls and parking total $24.00:

Vehicle	Gallons	Fuel cost	Total
Sedan, 32 mpg	18.75	$63.75	$87.75
SUV, 22 mpg	27.27	$92.73	$116.73

Taking the sedan saves $28.98. Split between four people, the sedan's total is $21.94 each. Per mile, fuel costs $0.11 in the sedan and $0.15 in the SUV — handy for comparing with a train fare or a rental car's daily rate.

In the UK, petrol is sold by the liter but economy is quoted in imperial mpg. Multiply the liter price by 4.54609 to get a price per imperial gallon: £1.38 a liter is £6.27 a gallon. A 250 km drive then costs £21.66 at 45 mpg and £17.72 at 55 mpg.

L/100km, US mpg and imperial mpg

The same mpg in liters per 100 km

mpg	US gallons → L/100km	Imperial gallons → L/100km
20	11.8	14.1
25	9.4	11.3
30	7.8	9.4
40	5.9	7
50	4.7	5.6

An imperial gallon holds about 20% more than a US gallon, so a UK mpg figure looks better than the US figure for the same car. Copy the unit from wherever you got the number.

Reading the units

L/100km is fuel used, so lower is better. It's used in Europe, Canada, Australia and most of the world. mpg is distance per fuel, so higher is better.
Exact definitions: 1 mile = 1.609344 km, 1 US gallon = 3.785411784 liters and 1 imperial gallon = 4.54609 liters.
mpg hides big savings at the low end. Going from 20 to 25 mpg saves more fuel per mile than going from 40 to 50, because fuel used is 1 ÷ mpg. L/100km shows this directly, as the table does.
Official figures are lab ratings. Real-world use is often higher with highway speeds, heavy loads, roof boxes, air conditioning or cold weather, so add a margin for a budget.
Electric cars fit the same math: choose L/100km, enter kWh per 100 km and the price per kWh.

For the most accurate trip budget, measure your own economy: fill the tank, reset the trip meter, drive normally, and at the next fill-up divide the distance by the fuel you put in (for mpg) or the fuel by the distance × 100 (for L/100km). That figure reflects your driving, your load and your roads, which the official rating can't. For a long drive with mountain passes or a heavy trailer, run the calculator a second time with a worse figure to see the range.

Sources: NIST Handbook 44, Appendix C (units of measurement); UK Weights and Measures Act 1985, Schedule 1; US EPA and DOE, fueleconomy.gov. Checked 15 October 2026.

Frequently asked questions

How do I calculate the fuel cost of a trip?+

Work out the fuel used, then multiply by the price. In L/100km, fuel = distance × consumption ÷ 100: a 500 km drive at 7 L/100km uses 35 liters, which costs €63.00 at €1.80 a liter. In mpg, fuel = miles ÷ mpg.

How do I work out fuel cost per mile or per kilometer?+

Divide the fuel price by mpg, or multiply L/100km by the price and divide by 100. At $3.40 a gallon, a 32 mpg car costs 10.6 cents a mile; at €1.80 a liter, a car using 7 L/100km costs 12.6 cents a kilometer. Tolls, maintenance and other running costs come on top.

How do I find my car's real fuel economy?+

Fill the tank and reset the trip meter. At the next fill-up, note the distance and how much fuel the tank took. Miles ÷ gallons gives mpg — 350 miles on 11.2 gallons is 31.25 mpg — and liters × 100 ÷ km gives L/100km. Average a few tanks for a steadier figure than the dashboard estimate.

How do I split gas money for a road trip?+

Divide the total cost by the number of people sharing it. The 300-mile-each-way trip above costs $87.75 with tolls and parking, so four people pay $21.94 each. The calculator gives the total; split it yourself or use the Tip Calculator with the tip set to 0 to split it by uneven shares.

Can I enter the distance in miles?+

Yes. Set "Distance unit" to miles and enter the one-way distance in miles — no conversion needed (300 miles is 482.8 km). Efficiency can be in L/100km, US mpg or imperial mpg with either distance unit; the calculator converts between them.

How much does a road trip cost in gas?+

A 300-mile drive each way (600 miles round trip) in a 32 mpg car uses 18.8 US gallons. At $3.40 a gallon that's $63.75, or $87.75 with $24.00 of tolls and parking.

What's the difference between US and imperial mpg?+

The gallon. A US gallon is 3.785 liters and an imperial gallon 4.546 liters, so the same mpg figure means different fuel use. 500 km at 40 mpg uses 7.77 gallons either way, but that's 29.4 liters in US gallons and 35.3 liters in imperial ones. Enter the price per the same gallon you chose.

How do I compare the fuel cost of two cars?+

Enter each car's efficiency as Vehicle 1 and Vehicle 2, using the same unit. On that trip of 300 miles each way, a 22 mpg SUV costs $92.73 in gas against $63.75 for the 32 mpg car — $28.98 more. Tolls and extras are added to both.

How do I convert mpg to L/100km?+

Divide 235.215 by US mpg, or 282.481 by imperial mpg. 30 US mpg is about 7.8 L/100km; 30 imperial mpg is about 9.4 L/100km. The same numbers work backwards: 235.215 ÷ L/100km gives US mpg.

Can I use it for an electric car?+

Yes, with a trick: choose L/100km, enter consumption in kWh per 100 km and the price per kWh. The arithmetic is the same. 300 km at 17 kWh/100km is 51 kWh, which costs $8.16 at $0.16 per kWh. Results are still labeled as fuel.

Does it include wear, insurance or depreciation?+

No. It counts fuel plus the tolls, parking and other costs you enter for the whole trip. Tires, maintenance, insurance and depreciation also cost money per mile, so the full cost of driving is higher than the fuel cost.

Is anything I enter saved or sent?+

No. Distance, efficiency and prices are calculated in your browser and are not stored or uploaded. Fuel prices aren't looked up; you enter your own.