QuickCalculators estimates trip fuel cost from distance, fuel efficiency, and price per unit volume, with conversions among miles per gallon, litres per 100 km, and kilometres per litre, using the US gallon by default. Enter distance as a known length; for place-to-place mileage first, use the mileage calculator on this site, then bring that distance here for unit-accurate cost.
Estimate the fuel cost of a trip
Trip fuel cost equals (distance ÷ efficiency) × price when efficiency is distance per volume, or distance × (efficiency/100) × price when efficiency is L/100 km. Fuel Cost Calculator applies the matching formula for the selected unit set and can scale a one-way distance to a round trip.
Cost per mile or kilometre appears as a secondary line when distance is nonzero.
Example: 500 miles at 28 mpg and $3.40 per US gallon uses 500 ÷ 28 gallons, then multiplies by 3.40. Real-world economy is often lower than a rated figure because of traffic, speed, and load. Treat the estimate as planning math, not a receipt.
Convert between fuel efficiency units
Efficiency conversions must respect whether the unit rises or falls when fuel use improves. QuickCalculators converts mpg, L/100 km, and km/L with the correct identities rather than a single scale factor. US gallon mode is the default volume basis on this page unless imperial gallon is selected.
A vehicle at 30 mpg US is near 7.84 L/100 km because 235.215 ÷ 30 ≈ 7.84. Kilometres per litre rises when economy improves, similar in direction to mpg. Keeping the unit family consistent across distance and price avoids mixed-unit errors.
Avoid this common mistake
Miles per gallon and litres per 100 km run in opposite directions. Higher mpg is better; higher L/100 km is worse. The conversion is 235.215 ÷ mpg for US gallons to L/100 km, not a proportional scale factor that preserves "higher means better." Mixing those intuitions flips which vehicle looks cheaper to run.
A drop from 10 L/100 km to 8 L/100 km is an improvement, even though the number fell. An increase from 25 mpg to 30 mpg is also an improvement. The calculator's conversion panel keeps both scales labeled so the directionality stays visible.
Compare the US and imperial gallon
The US gallon is about 3.785 litres; the imperial gallon is about 4.546 litres. The same numeric mpg is therefore not the same physical economy across those gallon definitions. Fuel Cost Calculator names which gallon is active when efficiency uses miles per gallon.
Price per litre versus price per gallon must match the volume unit in the efficiency field. Converting price when switching gallon systems keeps the cost identity intact. Cross-border trip planning often needs that explicit gallon choice.
Frequently asked questions
How do you calculate fuel cost for a trip?
To calculate fuel cost for a trip, divide distance by distance-per-volume efficiency and multiply by price, or multiply distance by L/100 km efficiency over 100 and then by price per litre. Round trips double a one-way distance when that option is selected. The page runs the formula for the chosen units.
How much fuel does a 500 mile trip use?
How much fuel a 500 mile trip uses equals 500 divided by mpg in gallons for mpg-based efficiency. At 25 mpg the trip uses 20 gallons before price enters. At L/100 km rates, convert distance to kilometres first, then apply the metric formula.
How do you convert mpg to L/100 km?
To convert US mpg to L/100 km, compute 235.215 ÷ mpg. For 30 mpg the result is about 7.84 L/100 km. Imperial mpg uses a different constant because the gallon size differs.
What is the difference between a US and an imperial gallon?
A US gallon is about 3.785 litres and an imperial gallon is about 4.546 litres. Miles per gallon figures are not interchangeable across those definitions without conversion. This calculator defaults to the US gallon unless imperial is chosen.
Why is real-world fuel economy lower than the rated figure?
Real-world fuel economy is often lower than the rated figure because of speed, traffic, weather, load, and driving style. Rated tests follow controlled cycles. Planning with a slightly lower efficiency than the sticker is a common practical adjustment.
How do you work out cost per mile?
To work out cost per mile, divide total fuel cost by trip miles, or divide price per gallon by mpg for a direct dollars-per-mile rate in US units. Cost per kilometre uses the metric counterparts. The secondary output on this page reports that unit cost when distance is set.
Summary
The calculator prices a trip from distance, efficiency, and fuel price, defaulting to the US gallon and converting among mpg, L/100 km, and km/L. Higher mpg is better while higher L/100 km is worse, with US mpg to L/100 km using 235.215 ÷ mpg.
Mileage tools find distance between places; this page takes distance as an input for unit-accurate cost. US and imperial gallons differ in volume, so mpg labels must name which gallon applies.