Four inputs form a reproducible fuel budget
Begin with the distance the vehicle is expected to travel, not the straight-line gap between endpoints. Apply the trip-type multiplier once: a round trip is normally twice the entered one-way distance, while a one-way estimate is not. Divide the resulting distance by an economy expressed in matching distance-per-volume units, then multiply the required fuel by the entered price per that same volume unit.
For example, 300 miles at 30 miles per U.S. gallon requires an estimated 10 U.S. gallons. At $3.60 per gallon, the fuel line is $36. The arithmetic is conditional on all three assumptions; it does not fetch today's station price or know which roads will be driven. If only city coordinates are known, the city distance calculator can supply an orientation estimate, but a route planner is still needed before budgeting a road journey.
US, metric, and custom modes must remain internally consistent
US distance-per-volume
Enter miles, miles per U.S. gallon, and price per U.S. gallon. Do not silently use an imperial-gallon economy figure with a U.S.-gallon price.
Metric consumption
For litres per 100 kilometres, fuel equals distance × consumption ÷ 100. Lower L/100 km denotes better economy, so the formula direction differs from MPG.
Custom combinations
Choose each unit explicitly and verify the conversion path. The exact litre, kilometre, mile, and U.S.-gallon relationships are deterministic; the estimated economy and future price are not.
Separate observed efficiency from the planning scenario
- Prefer a representative economy value
A label estimate offers a standardized reference. Several complete refill intervals may better represent the specific driver and vehicle. Use the mileage calculator to derive that observed value from paired odometer readings and fuel added.
- Record the price date and place
Fuel prices change and may differ along a route. The calculator uses exactly the price entered; update it rather than presenting an old scenario as a live quote.
- Run scenarios instead of hiding uncertainty
A low, central, and high economy or price scenario shows the budget range. This is more informative than adding decimals to one uncertain point estimate.
Driving conditions can move the real result away from the estimate
- Traffic, speed, grade, weather, cold starts, payload, towing, idling, and accessory loads affect actual consumption. A single economy input cannot model their route-by-route detail.
- A detour or stop sequence changes driven distance. Update the route total rather than assuming a fixed percentage will cover every itinerary change.
- Electric energy, charging loss, and time-based charging tariffs are outside a liquid-fuel division. A different energy model is required for an EV trip.
- Tyre condition matters operationally, but pressure must follow vehicle and tyre safety guidance. The tire dimensions calculator can compare nominal size geometry, but it cannot prescribe pressure or justify changing inflation merely to force a target MPG result.
Fuel is only one line in a complete trip cost
Add tolls, parking, ferries, permits, lodging, and other charges separately, using current route and facility sources for tolls rather than a generic rate. Maintenance, depreciation, finance, insurance, and the value of time need their own assumptions and should not be smuggled into a fuel price.
Save the route distance, one-way or return selection, economy value and provenance, volume convention, fuel price and date, plus the final rounding rule. That audit trail turns a disposable answer into a scenario another traveller can update. It also makes clear that this page estimates consumption and expense; it does not guarantee range, reserve level, station availability, or a safe refuelling plan.