Travel quantities
Price a road trip with the right distance and gallon convention
The easiest fuel-budget mistake is not complicated arithmetic. It is using the outbound distance for a return trip, or reading an MPG figure without checking which gallon it means.
Make the journey boundary explicit
Enter the distance you actually want to price. For a return journey, include both directions and planned pickups. The calculator does not fetch a road route, add a return leg or know how much sightseeing you intend to do.
An additional-distance allowance can represent a deliberately chosen detour scenario. It does not model traffic, idling, speed, towing, temperature or terrain. Use measured consumption for a comparable trip if you have it, and test a worse-consumption case separately.
Work the 300 km example
The default is an illustrative 300 km trip, plus a 10% distance allowance. That makes 330 km. At 7 litres per 100 km, fuel required is 23.1 litres. With an entered price of USD 1.50 per litre, fuel costs USD 34.65.
Fuel quantity is calculated before the final cost rounds to the selected currency precision. The example tariff is not a current regional pump price. Enter the offered per-litre price; tolls, parking, lodging, maintenance and vehicle wear remain outside the fuel-only result.
Choose US or Imperial MPG deliberately
A US gallon is 3.785411784 litres; an Imperial gallon is 4.54609 litres. A mile is 1.609344 kilometres. The tool converts the entered distance and selected MPG convention before applying the per-litre price.
For an intentionally simple unit check, one mile at one mile per US gallon consumes one US gallon. Switching to one mile per Imperial gallon changes the litres even though both displayed MPG numbers are 1. This is why an unlabeled MPG comparison can mislead.
Use scenarios rather than a false exact trip bill
Keep the base route beside a longer-route case on your canvas. Change only one assumption at a time so the difference has a clear cause. If actual consumption becomes available, retain the original inputs and record the measurement date before revising them.
An estimate with three decimal places of litres is still based on the distance and economy assumptions entered. It is not evidence that the real car will consume fuel to that precision.
Primary references
Authored 2026-10-29. Arithmetic examples are covered by local regression tests. New workflow guides remain outside the indexing allowlist pending editorial and applicable specialist review. Examples use the assumptions stated here; authority guidance can change.