How do I calculate the fuel cost of a trip?

Work out the fuel used, then multiply by the price per unit of fuel. With MPG, fuel in gallons is miles ÷ MPG: 300 mi at 30 MPG is 10 US gal. At a hypothetical $4.00 per US gallon that is $40.00. With L/100 km, litres are kilometres × L/100 km ÷ 100: 500 km at 8 L/100 km is 40 L, which at 2.00 per litre (also hypothetical) is $80.00.

How do I work out my gas mileage from a fill-up?

Fill the tank, note the distance on the trip meter, and at the next fill-up divide the distance by the fuel you added. 350 miles on 11.2 US gallons is 31.25 MPG (US), 7.53 L/100 km, 37.53 MPG (UK) and 13.29 km/L. Fill to the same point each time for a fair figure, and average several fill-ups, since a single one can be off by a few percent.

How do I convert MPG to L/100 km?

Divide 235.21 by the MPG (US) figure: L/100 km = 235.21 ÷ MPG. The constant is 100 × 3.785411784 ÷ 1.609344. So 30 MPG (US) is 7.84 L/100 km. The same formula converts back, because 30 MPG and 7.84 L/100 km are the same economy: 235.21 ÷ 7.84 is about 30. For imperial MPG the constant is 282.48.

Why is UK MPG a bigger number than US MPG?

The imperial gallon (4.54609 L) is larger than the US gallon (3.785411784 L), so the same car goes further on one imperial gallon. MPG (UK) is MPG (US) × 4.54609 ÷ 3.785411784, about 1.2 times as much: 30 MPG (US) is 36.03 MPG (UK). The car is the same; only the gallon differs. Always check which gallon a figure uses.

Is a higher or lower number better?

It depends on the unit. MPG and km/L measure distance per fuel, so higher is better. L/100 km measures fuel per distance, so lower is better. The table above lines the units up.

How does the round trip option work?

It doubles the distance you typed, so the fuel and the cost double too: $20.00 one way becomes $40.00 there and back for the example. Untick it for a one-way trip, or type the full distance yourself.

How is the cost split between people?

The total is rounded to a cent once, then divided by the number of people with a remainder in cents, so some people pay one cent more and the shares add up to the total exactly. For the example, $40.00 among 3 people is $13.33 to $13.34 each, and the tool says how many people pay the extra cent.

Does the calculator know current fuel prices?

No. It does not fetch or store any prices; you type the price you pay. The example price on this page is made up to show how the sums work and is not a real or current price. Prices differ by place and change often, so use your own.

What about electric cars?

Electric vehicles are out of scope here. They are rated in kWh per 100 km or miles per kWh, and charging prices work differently, so this tool only covers liquid fuel.

How accurate is the estimate?

The arithmetic is exact, but real fuel use depends on speed, load, weather, traffic and driving style, so the result is an estimate. Use a mileage figure from your own recent driving for the best answer. Nothing you type is stored or sent anywhere.

Gas Mileage & Fuel Cost Calculator

To find what a trip costs, divide the distance by your fuel economy to get the fuel used, then multiply by the price: a 300 mi round trip at 30 MPG (US) uses 10 US gal (37.85 L), which at a hypothetical $4.00 per US gallon costs $40.00, or $13.33 or $13.34 each for 3 people. Enter the distance in miles or kilometres, your economy in MPG (US or UK), L/100 km or km/L, and the price per US gallon, imperial gallon or litre, and the tool shows the fuel and the cost. It can also work out your mileage from a fill-up (distance driven and fuel added) and convert between MPG (US), MPG (UK), L/100 km and km/L. Conversions use the exact definitions of the gallon and the mile, and the cost shares add up to the total to the cent.

Updated 2026-10-03Runs in your browser: nothing you enter is uploadedHow this tool works

Trip fuel cost

Each person pays $13.33 or $13.34

37.85 L (10 US gal) over 300 mi at 30 MPG (US), $40.00 in total, split 3 ways.

Total distance (round trip): 300 mi (482.8 km)
Fuel economy: 30 MPG (US) = 7.84 L/100 km
Fuel used: 37.85 L
Fuel used (gallons): 10 US gal
Fuel cost: $40.00
Cost per mile: $0.133
Cost per km: $0.083
Cost per person: $13.33 to $13.34

Of the 3 people, 1 pays $13.34, one cent more than the other 2 ($13.33), because $40.00 does not divide evenly. The shares add up to the total exactly. The price is the one you entered, not a current or typical fuel price.

Mileage from a fill-up

31.25 MPG (US), 7.53 L/100 km

350 mi on 11.2 US gal.

MPG (US): 31.25
MPG (UK, imperial): 37.53
L/100 km: 7.53
km/L: 13.29

A lower L/100 km is better; a higher MPG or km/L is better.

MPG and L/100 km converter

30 MPG (US) = 36.03 MPG (UK)

Also 7.84 L/100 km and 12.75 km/L.

MPG (US): 30
MPG (UK, imperial): 36.03
L/100 km: 7.84
km/L: 12.75

A lower L/100 km is better; a higher MPG or km/L is better.

MPG (US) in L/100 km, MPG (UK) and km/L

Each row converts the MPG (US) figure with the exact gallon and mile definitions; a lower L/100 km means less fuel.
MPG (US)	L/100 km	MPG (UK)	km/L
10	23.52	12.01	4.25
15	15.68	18.01	6.38
20	11.76	24.02	8.5
25	9.41	30.02	10.63
30	7.84	36.03	12.75
35	6.72	42.03	14.88
40	5.88	48.04	17.01
45	5.23	54.04	19.13
50	4.7	60.05	21.26
55	4.28	66.05	23.38
60	3.92	72.06	25.51

The constants behind every conversion

Three exact definitions; every other factor on this page is calculated from them.
Quantity	Value	Where it is used
1 US gallon	3.785411784 L (exact)	MPG (US), prices per US gallon
1 imperial gallon	4.54609 L (exact)	MPG (UK), prices per imperial gallon
1 mile	1.609344 km (exact)	Every mile and kilometre conversion
L/100 km × MPG (US)	235.21 (100 × 3.785411784 ÷ 1.609344)	L/100 km = this ÷ MPG (US)
L/100 km × MPG (UK)	282.48 (100 × 4.54609 ÷ 1.609344)	L/100 km = this ÷ MPG (UK)

How to calculate fuel cost for a trip

Enter the distance. Type the distance and choose miles or kilometres. Tick “Round trip” to count the way back too: 150 mi each way is 300 mi.
Enter your fuel economy. Type your economy and pick its unit: MPG (US), MPG (UK), L/100 km or km/L. The example is 30 MPG (US), which is 7.84 L/100 km. If you do not know it, use the fill-up section below.
Enter the fuel price. Type the price you pay and choose per US gallon, per imperial gallon or per litre. The example uses a made-up $4.00 per US gallon; replace it with the price at your pump.
Add people if you are sharing. Set the number of people to split the cost. $40.00 among 3 is $13.33 to $13.34: the shares differ by one cent and add up to the total exactly.
Read the fuel and the cost. The result shows the fuel used in litres and gallons, the cost, and the cost per mile and per kilometre. For the example that is 37.85 L and $40.00.

Frequently asked questions

How do I calculate the fuel cost of a trip?: Work out the fuel used, then multiply by the price per unit of fuel. With MPG, fuel in gallons is miles ÷ MPG: 300 mi at 30 MPG is 10 US gal. At a hypothetical $4.00 per US gallon that is $40.00. With L/100 km, litres are kilometres × L/100 km ÷ 100: 500 km at 8 L/100 km is 40 L, which at 2.00 per litre (also hypothetical) is $80.00.
How do I work out my gas mileage from a fill-up?: Fill the tank, note the distance on the trip meter, and at the next fill-up divide the distance by the fuel you added. 350 miles on 11.2 US gallons is 31.25 MPG (US), 7.53 L/100 km, 37.53 MPG (UK) and 13.29 km/L. Fill to the same point each time for a fair figure, and average several fill-ups, since a single one can be off by a few percent.
How do I convert MPG to L/100 km?: Divide 235.21 by the MPG (US) figure: L/100 km = 235.21 ÷ MPG. The constant is 100 × 3.785411784 ÷ 1.609344. So 30 MPG (US) is 7.84 L/100 km. The same formula converts back, because 30 MPG and 7.84 L/100 km are the same economy: 235.21 ÷ 7.84 is about 30. For imperial MPG the constant is 282.48.
Why is UK MPG a bigger number than US MPG?: The imperial gallon (4.54609 L) is larger than the US gallon (3.785411784 L), so the same car goes further on one imperial gallon. MPG (UK) is MPG (US) × 4.54609 ÷ 3.785411784, about 1.2 times as much: 30 MPG (US) is 36.03 MPG (UK). The car is the same; only the gallon differs. Always check which gallon a figure uses.
Is a higher or lower number better?: It depends on the unit. MPG and km/L measure distance per fuel, so higher is better. L/100 km measures fuel per distance, so lower is better. The table above lines the units up.
How does the round trip option work?: It doubles the distance you typed, so the fuel and the cost double too: $20.00 one way becomes $40.00 there and back for the example. Untick it for a one-way trip, or type the full distance yourself.
How is the cost split between people?: The total is rounded to a cent once, then divided by the number of people with a remainder in cents, so some people pay one cent more and the shares add up to the total exactly. For the example, $40.00 among 3 people is $13.33 to $13.34 each, and the tool says how many people pay the extra cent.
Does the calculator know current fuel prices?: No. It does not fetch or store any prices; you type the price you pay. The example price on this page is made up to show how the sums work and is not a real or current price. Prices differ by place and change often, so use your own.
What about electric cars?: Electric vehicles are out of scope here. They are rated in kWh per 100 km or miles per kWh, and charging prices work differently, so this tool only covers liquid fuel.
How accurate is the estimate?: The arithmetic is exact, but real fuel use depends on speed, load, weather, traffic and driving style, so the result is an estimate. Use a mileage figure from your own recent driving for the best answer. Nothing you type is stored or sent anywhere.

How it works

All conversions come from three exact definitions: 1 US gallon = 3.785411784 L, 1 imperial gallon = 4.54609 L and 1 mile = 1.609344 km. Economy is held as litres per 100 km. For MPG the factor is calculated, not typed in: L/100 km = 100 × (litres per gallon) ÷ (km per mile) ÷ MPG, which is 235.21 ÷ MPG (US) and 282.48 ÷ MPG (UK) to two decimals; km/L = 100 ÷ (L/100 km). A trip’s fuel is distance in km × L/100 km ÷ 100, doubled for a round trip. The cost is that fuel, divided by the litres in the price’s unit, times the price you typed, rounded to a whole cent once. Mileage from a fill-up is fuel in litres × 100 ÷ distance in km, shown in all four units. To split, the cost in cents is divided by the number of people with a remainder in cents; that many people pay one cent more, so the shares add up to the total exactly. Displayed figures are rounded to two decimals (the cost per mile and per km to three), while the calculations keep full precision. The calculator holds no fuel prices and makes no claim about what fuel costs; the example price is hypothetical. Electric vehicles are not covered. Everything runs in your browser and nothing you type is sent anywhere.

Sources

All tools Home & DIY calculators