How TripFuel estimates your fuel cost
A transparent estimate from distance, consumption and price.
Method and worked examples checked November 7, 2026.
The core calculation
TripFuel converts the journey distance to kilometres, the fuel economy to litres per kilometre and the price to a cost per litre. Estimated fuel used equals distance × consumption. Estimated cost equals fuel used × price. Converting to shared units allows, for example, a distance in miles to be combined with fuel sold by the litre.
- For L/100 km: litres used = kilometres × L/100 km ÷ 100.
- For km/L: litres used = kilometres ÷ km/L.
- For MPG with matching gallon units: gallons used = miles ÷ MPG, then cost = gallons × price per gallon.
A US example, checked step by step
Enter 300 miles, 30 US MPG and $3.60 per US gallon. Leave the return option off. The journey uses 300 ÷ 30 = 10 US gallons, giving an estimated cost of $36. With three people, each person's share is $12.
If you repeat that same journey twice, the combined cost is $72 and each person's share across both trips is $24. The single-trip result remains $36. This separates the cost of one journey from the total for a repeated plan.
Checking Include return doubles the entered distance before calculating fuel. With the same settings, one round trip costs $72. Combining that option with two trips means two round trips: 1,200 miles in total and $144 for everyone. Do not select return if the entered distance already includes both directions.
A metric example
For a 200 km journey at 7.5 L/100 km, estimated consumption is 200 × 7.5 ÷ 100 = 15 litres. At 1.60 per litre, the estimated cost is 24.00 in the selected currency. If your real consumption is 9 L/100 km instead, the estimate becomes 18 litres and 28.80. That difference comes from consumption, not rounding.
Which gallon, which currency?
The implementation uses 1 mile = 1.609344 km, 1 US gallon = 3.785411784 litres, and 1 Imperial gallon = 4.54609 litres. US and Imperial MPG are therefore different measurements. Select the unit used by the source of your economy figure and the separate unit used by the fuel price.
NIST's conversion tables are a reference for these unit relationships. Our US versus Imperial MPG guide explains a common source of mismatches.
The currency selector changes the display label and number formatting. It does not obtain exchange rates or convert your price. Enter a price already expressed in the currency you intend to use. Prices in these examples are hypothetical, not live pump quotes.
Limits and rounding
Distances may range from zero to 100,000,000; economy must be greater than zero and no more than 10,000; and fuel price must be between zero and 100,000. Splits accept 1 to 99 whole people, while repeats accept 1 to 1,000 whole trips. These are input guardrails, not statements that every permitted combination is physically realistic.
The calculator uses unrounded intermediate values and formats the results for display. A low cost per mile can look coarse when rounded to currency precision. Use the total journey estimate for budgeting rather than multiplying a rounded displayed unit cost back out.
What is outside the estimate
This is a fuel-only estimate. It does not obtain a route, local prices or your vehicle's actual consumption, and it excludes tolls, parking, maintenance, depreciation and charging costs. Traffic, idling, load and weather can change real fuel use. Compare a realistic and a less-efficient scenario before committing to a budget.
Copy and download include the entered units, trip count and per-person totals. Inputs are not saved as a trip history. For a discrepancy, send the values and unit selections. Open the fuel cost calculator →