Miles per gallon is the distance driven divided by the US gallons of fuel used to cover it. Fill the tank, reset the trip meter, drive, then refill: 300 miles on 10 gallons is 30 MPG, which equals 7.84 litres per 100 km or about 36 imperial MPG.
Drivers checking whether a car still returns its rated economy, fleet managers comparing vans, and anyone budgeting a long drive all need the same number: miles per gallon from a real fill-up. Enter the distance from the trip meter and the gallons it took to refill the tank, and the calculator returns US MPG along with the metric figures used outside the US (litres per 100 km and km per litre), the UK imperial MPG and gallons per 100 miles. Add a pump price and it also shows what the fuel for that distance cost and the cost per mile. One limit: a single tank is a noisy sample, because pumps click off at slightly different levels; averaging three or more fill-ups gives a steadier figure.
Type the miles shown on the trip meter since your last full tank.
Type the US gallons the pump delivered when you filled the tank back up.
The optional price per gallon adds the fuel cost for the distance and the cost per mile.
Below the MPG figure you get L/100 km, km/L, imperial MPG and the working for each.
Result Miles per gallon (US): 30
Litres per 100 km: 7.84
Kilometres per litre: 12.75
UK (imperial) MPG: 36
Gallons per 100 miles: 3.33
Fuel cost for the distance: —
Fuel cost per mile: —
A typical midsize sedan figure: 30 US MPG equals 7.84 litres per 100 km and about 36 imperial MPG.
Result Miles per gallon (US): 27.5
Litres per 100 km: 8.55
Kilometres per litre: 11.69
UK (imperial) MPG: 33
Gallons per 100 miles: 3.64
Fuel cost for the distance: 52.5
Fuel cost per mile: 0.127
412.5 ÷ 15 gives 27.5 MPG; the 15 gallons cost $52.50, about 12.7 cents for every mile.
MPG = d ÷ g; L/100 km = 235.215 ÷ MPG; cost per mile = p ÷ MPG
dgpFuel economy in the US is distance per unit of fuel, so MPG is simply miles divided by gallons. The metric figure is inverted: fuel per distance. Converting uses exact definitions, 1 mile = 1.609344 km and 1 US gallon = 3.785411784 litres, which give the constant 235.215 that fueleconomy.gov publishes. An imperial gallon is 4.54609 litres, so UK MPG is US MPG multiplied by about 1.201.
EPA ratings come from standardised lab cycles. Real driving adds cold starts, air conditioning, roof racks, under-inflated tyres, idling and higher motorway speeds, each of which costs a few percent. A gap of 10 to 20 percent below the combined rating is common and does not by itself mean something is wrong.
Divide 235.215 by the US MPG. For example, 30 MPG is 235.215 ÷ 30 = 7.84 L/100 km. Because the metric figure measures fuel per distance, a lower number is better, the opposite of MPG.
A UK imperial gallon holds 4.54609 litres while a US gallon holds 3.785 litres, about 20 percent less. The same car covers more miles on the bigger gallon, so 30 US MPG reads as roughly 36 UK MPG.
Three or more full tanks give a far more stable number than one. Add up all the miles and all the gallons across those tanks and enter the totals, rather than averaging the individual MPG figures, which over-weights short tanks.
It is the US equivalent of L/100 km and shows fuel used directly. Going from 10 to 20 MPG saves 5 gallons per 100 miles, while going from 30 to 40 MPG saves only 0.83 gallons, which is why the EPA label now shows this figure as well.
No. It is only the price per gallon divided by MPG. Insurance, depreciation, tyres and servicing usually add more per mile than fuel does, so treat this as the fuel share of running costs.
Using this tool in an assignment, article or report? Copy a citation, or a link for your website.
Tools Directory Editorial Team. (2026, October 9). Miles per Gallon Calculator. Tools Directory. Retrieved October 26, 2026, from https://tools.milunir.com/automotive/vehicle-ownership-costs/miles-per-gallon-calculator/
Tools Directory Editorial Team. “Miles per Gallon Calculator.” Tools Directory, 9 Oct. 2026, https://tools.milunir.com/automotive/vehicle-ownership-costs/miles-per-gallon-calculator/. Accessed 26 Oct. 2026.
Tools Directory Editorial Team. “Miles per Gallon Calculator.” Tools Directory. Last modified October 9, 2026. Accessed October 26, 2026. https://tools.milunir.com/automotive/vehicle-ownership-costs/miles-per-gallon-calculator/.
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