Fuel Cost Calculator – Gas Cost for a Trip (mpg, km/L)

Fuel Cost Calculator

Fuel cost is the distance divided by your fuel economy, times the price of fuel. A 300-mile trip in a car that gets 28 mpg uses 10.71 gallons, which costs $44.46 at $4.15 a gallon. Enter miles or kilometres and mpg, km/L or L/100 km.

By the Calculators With Steps team · Updated November 10, 2026 · How we check our math

How to use the fuel cost calculator

Enter the trip distance and choose miles or kilometres. Use the distance from your map app’s route.
Enter your car’s fuel economy and pick the unit you know: mpg (US), mpg (UK), km per litre or litres per 100 km.
Enter the fuel price and whether it is per US gallon, per litre or per imperial gallon. The currency menu covers dollars, rupees, pounds, euros and more.
Tick round trip to double the distance, and enter the number of people if you are splitting the cost.

You get the total cost, the fuel needed in gallons and litres, the cost per mile, per km and per 100 miles, and each person’s share.

Fuel cost formula

Fuel used = distance ÷ fuel economy

Fuel cost = fuel used × price per unit of fuel

With L/100 km the formula flips, because that unit is fuel per distance: litres used = distance in km × L/100 km ÷ 100.

The calculator converts every input to kilometres, km per litre and price per litre, so you can mix units freely, for example a distance in miles with a price per litre.

Worked example: a road trip

A 300-mile drive each way in a car rated at 28 mpg, with regular gas at $4.15 a gallon (the U.S. average in the first week of November 2026, according to the EIA):

Step	Working	Result
Distance	300 × 2 (round trip)	600 miles
Fuel used	600 ÷ 28	21.43 gallons
Cost	21.43 × $4.15	$88.93
Per person (4 people)	88.93 ÷ 4	$22.23
Cost per mile	4.15 ÷ 28	$0.148

Examples in India and the UK

India (petrol in km/L). A 500 km trip in a car that gives 15 km/L uses 500 ÷ 15 = 33.33 litres. At ₹100 a litre the petrol costs about ₹3,333, or ₹6.67 per km. Switch the currency to INR, the distance to kilometres and the price to per litre.

UK (mpg with price per litre). A 200-mile journey in a car that does 45 mpg (UK) uses 20.2 litres. At £1.40 a litre that costs £28.29. The calculator handles the mix of miles, imperial gallons and litres for you.

Converting fuel economy units

mpg (US)	mpg (UK)	km/L	L/100 km
20	24.0	8.5	11.76
28	33.6	11.9	8.40
30	36.0	12.75	7.84
40	48.0	17.0	5.88

To convert by hand: L/100 km = 235.215 ÷ mpg (US), and km/L = mpg (US) × 0.425144. Lower L/100 km and higher mpg are better. The unit converter converts any of these in either direction.

Monthly commuting cost

Gas for a regular commute adds up faster than a single trip suggests. For a 30-mile round trip on 21 workdays (630 miles a month) at $4.15 a gallon:

Fuel economy	Gallons a month	Cost a month	Cost a year
20 mpg	31.5	$130.73	$1,568.70
28 mpg	22.5	$93.38	$1,120.50
30 mpg	21	$87.15	$1,045.80
40 mpg	15.75	$65.36	$784.35

Moving from a 20 mpg vehicle to a 40 mpg one halves the fuel bill on the same commute.

Why your real cost may differ

Rated vs real economy. Official ratings come from standard tests. High highway speeds, city stop-and-go, air conditioning, cold weather, roof boxes and heavy loads all cut real-world mpg.
Price changes along the route. Fuel prices vary a lot between states, cities and highway stations. Use an average of the prices you expect to pay.
Detours and idling. Add a few percent for wrong turns, traffic and stops.

Your trip computer is the best guide to your own car’s economy. FuelEconomy.gov lists official ratings and owner-reported figures for most U.S. models.

Comparing driving with other options

To compare a gasoline car with an electric one, work out the EV’s cost with the electricity cost calculator: kWh used per 100 miles multiplied by your price per kWh. To compare the full cost of owning a car, including the loan, use the auto loan calculator. Fuel is often only a fraction of the total.

Fuel Cost Calculator: frequently asked questions

How do I calculate gas cost for a trip?

Divide the trip distance by your car's mpg to get gallons, then multiply by the price per gallon. 300 miles ÷ 28 mpg = 10.71 gallons, and 10.71 × $4.15 = $44.46.

What is the gas cost per mile formula?

Cost per mile = price per gallon ÷ miles per gallon. At $4.15 a gallon and 28 mpg, each mile costs about $0.148, or $14.82 per 100 miles.

How do I calculate fuel cost per km?

Divide the price per litre by your km per litre. At ₹100 a litre and 15 km/L, each kilometre costs ₹6.67, so a 500 km trip uses 33.33 litres and costs about ₹3,333.

How do I calculate a round trip and split it between friends?

Double the one-way distance, work out the cost, then divide by the number of people. A 300-mile drive each way at 28 mpg and $4.15 a gallon costs $88.93 round trip, or $22.23 each for four people.

How much gas does it take to drive 100 miles?

100 miles ÷ your mpg. A 28 mpg car uses about 3.57 gallons (13.5 litres) per 100 miles, which costs $14.82 at $4.15 a gallon.

Why are UK mpg figures higher than US mpg?

A UK (imperial) gallon is 4.546 litres, about 20% more than a 3.785-litre US gallon, so the same car covers more miles per UK gallon. 1 mpg (UK) equals 0.833 mpg (US).

How do I calculate my monthly gas cost for commuting?

Multiply your daily round-trip miles by the days you drive, then divide by mpg and multiply by the price. A 30-mile round trip on 21 workdays is 630 miles; at 28 mpg and $4.15 a gallon that is 22.5 gallons and $93.38 a month.