Gas Cost Calculator

Work out how much gas a trip will cost from the distance, your car’s MPG and the price per gallon — round trip or one way, split between everyone in the car.

$62.50 in fuel

for 500 miles round trip at $3.50 per gallon · $31.25 each for 2 people

Fuel used

17.86 gal

67.6 liters

Cost per mile

12.5¢

7.8¢ per km

Per person

$31.25

split 2 ways

Fuel economy

28 MPG

= 8.401 L/100 km

Working

Round trip: 250 mi × 2 = 500 mi.
Fuel used: 500 mi ÷ 28 MPG = 17.857 gallons (67.597 L).
Cost: 17.857 gal × $3.50 per gallon = $62.50.
Cost per mile: $62.50 ÷ 500 mi = 12.5¢.
Split 2 ways: $62.50 ÷ 2 = $31.25 each.

Same trip, different car

Fuel used and cost for this trip at other fuel economies
Fuel economy	Fuel	Trip cost	Difference
15 MPG	33.33 gal	$116.67	+$54.17
20 MPG	25 gal	$87.50	+$25.00
25 MPG	20 gal	$70.00	+$7.50
28 MPG (yours)	17.86 gal	$62.50	—
30 MPG	16.67 gal	$58.33	−$4.17
35 MPG	14.29 gal	$50.00	−$12.50
40 MPG	12.5 gal	$43.75	−$18.75
50 MPG	10 gal	$35.00	−$27.50

How to use the gas cost calculator

Enter the distance of your trip — one way, then choose Round trip if you’re driving back — and your car’s fuel economy. Add the price you expect to pay per gallon and how many people are splitting the cost. The total, the fuel you’ll burn, the cost per mile and each person’s share update as you type.

Prefer metric? Switch the distance to kilometers, the fuel economy to liters per 100 km or the price to per liter — the number in the box is converted, so the trip stays the same and you can mix units freely. The table underneath shows what the same trip would cost in more or less efficient cars. Your inputs are kept in the page address, so you can send the link to whoever you’re splitting with.

The formula

gallons = miles ÷ MPG
cost    = gallons × price per gallon
per person = cost ÷ people        cost per mile = cost ÷ miles

metric: liters = km × (L/100 km) ÷ 100,   cost = liters × price per liter

The calculator converts between systems with the exact factors 1 mile = 1.609344 km and 1 US gallon = 3.785411784 liters. Fuel economy converts with L/100 km = 235.215 ÷ MPG, which also works the other way round.

Worked example

The calculator opens with a 250-mile drive each way, a car that gets 28 MPG, gas at an example $3.50 a gallon, and 2 people sharing:

Round trip: 250 × 2 = 500 miles.
Fuel: 500 ÷ 28 = 17.857 gallons (67.597 liters).
Cost: 17.857 × $3.50 = $62.50, or 12.5¢ a mile.
Split two ways: $31.25 each.

The same trip in a 40 MPG car uses 12.5 gallons and costs $43.75 — $18.75 less. In a 20 MPG truck it is 25 gallons and $87.50.

MPG to L/100 km

MPG (US)	L/100 km
15	15.68
20	11.76
25	9.41
30	7.84
35	6.72
40	5.88
50	4.7

Notice that L/100 km measures fuel used, so lower is better, while MPG measures distance, so higher is better. Going from 15 to 20 MPG saves far more fuel than going from 40 to 50 MPG over the same distance.

Getting the inputs right

Gas price. The U.S. Energy Information Administration publishes weekly average retail prices for the country, regions and some states and cities; prices at individual stations vary, so check along your route. The $3.50 default is an example, not a current price.
Your real MPG. The best number is your own: fill the tank, reset the trip meter, drive, and at the next fill-up divide the miles driven by the gallons it took. For a mostly-highway trip, the car’s highway rating from its window sticker or fueleconomy.gov is a reasonable stand-in.
Driving style and load. Fueleconomy.gov notes that aggressive driving can cut gas mileage by roughly 15% to 30% at highway speeds and that mileage usually drops quickly above 50 mph. Roof boxes, heavy loads and towing lower it too, so round your MPG down for a loaded road trip.

This is the fuel cost only: tolls, parking and wear on the car are extra. For an electric car, the electricity cost calculator works out charging costs, and if you are shopping for a new car, the auto loan calculator shows the monthly payment. To convert speeds for a trip abroad, see mph to km/h.

Frequently asked questions

How do I calculate the gas cost of a trip?

Divide the distance by your car’s miles per gallon to get the gallons used, then multiply by the price per gallon: cost = miles ÷ MPG × price. A 500-mile round trip in a car that gets 28 MPG uses 17.857 gallons; at $3.50 a gallon that is $62.50.

How do I split gas money for a road trip?

Work out the fuel cost for the whole trip — including the drive home — and divide by the number of people sharing. The example trip costs $62.50 in fuel, or $31.25 each for two people. Tolls and parking are extra; add them before you split.

How do I convert MPG to liters per 100 km?

Divide 235.215 by the MPG: 30 MPG is 235.215 ÷ 30 = 7.84 L/100 km. The same division converts back, so 8 L/100 km is 29.4 MPG. The constant comes from 100 × 3.785411784 liters per US gallon ÷ 1.609344 km per mile. MPG here means US gallons; the UK uses a larger imperial gallon.

Why is my real gas mileage lower than the sticker?

Driving style, speed, traffic, weather, cargo and the car’s condition all matter. Fueleconomy.gov notes that aggressive driving — speeding, rapid acceleration and hard braking — can lower gas mileage by roughly 15% to 30% at highway speeds and 10% to 40% in stop-and-go traffic, and that mileage usually drops quickly above 50 mph. For a trip estimate, use the MPG you actually get, or the highway rating for a highway trip.

Where can I find current gas prices?

The U.S. Energy Information Administration publishes average retail gasoline and diesel prices every week — nationally, by region and for some states and cities — in its Gasoline and Diesel Fuel Update. Prices at the pump near you can differ from the average, so check local stations along your route. This calculator doesn’t load live prices; the $3.50 default is only an example.

Last reviewed 25 September 2026 · Built and checked by the Reeliy team · How we test our tools

Gas Cost Calculator