Fuel Cost Calculator
Estimate trip gas expenses based on driving distance, fuel efficiency (MPG), and gas price per gallon.
Trip Cost Output
Per mile, not per tank
Fuel cost for a journey is distance divided by fuel economy, multiplied by price. The division flips depending on which economy measure you have: with miles per gallon you divide distance by MPG to get gallons, while with litres per 100 km you multiply distance by the figure and divide by 100. The two run in opposite directions — higher MPG is better, lower L/100km is better.
MPG is a deceptive scale, and this matters when comparing vehicles. Improving from 10 to 15 MPG saves more fuel over the same distance than improving from 30 to 50, because the relationship is reciprocal. Fuel consumed per distance, which is what L/100km measures directly, is the more honest comparison, and is why many countries use it.
Real-world economy typically falls below the official figure. Speed is the dominant factor, since aerodynamic drag rises with the square of velocity — sustained motorway speeds can cost 15-20% against a moderate cruise. Cold starts, short trips, roof boxes, underinflated tyres and heavy loads all add. For a full cost of driving, fuel is only part: depreciation, insurance, tyres and maintenance usually exceed it.
Frequently asked questions
How to calculate trip gas cost?
Total Gas Cost = (Total Distance / Vehicle MPG) × Price Per Gallon.
How do I calculate the fuel cost of a trip?
Divide the distance by your vehicle's fuel economy to get the fuel needed, then multiply by the price per unit. In metric, cost = distance / 100 x litres-per-100km x price per litre. Remember it is a round trip unless you are being collected.
How do I convert between MPG and litres per 100 km?
They are reciprocal, so 235.2 divided by MPG gives L/100km and vice versa for US gallons; use 282.5 for imperial gallons. Note that the relationship is not linear: improving from 15 to 20 MPG saves far more fuel over the same distance than improving from 40 to 45.
Why is my real fuel economy worse than the official figure?
Official figures come from standardised test cycles that understate real-world driving. Cold starts, short journeys, high speeds, air conditioning, roof racks, under-inflated tyres, heavy loads and stop-start traffic all reduce economy. A 10-20% shortfall against the sticker figure is normal - use your own measured consumption for any estimate that matters.