Mileage & Fuel Average Calculator
km/l, l/100km, and cost per km — plus tank-to-tank tracking across multiple fill-ups
Frequently Asked Questions
Vehicle fuel efficiency (mileage) can be estimated two different ways — a single-fill quick estimate from one tank of fuel, or a more accurate tank-to-tank calculation tracked across multiple fill-ups over time — and the two methods can genuinely disagree, with the tracked method generally being the more trustworthy one.
Why tank-to-tank tracking beats a single estimate
A single-fill estimate (distance covered divided by fuel used for one tank) is quick but vulnerable to one-off distortions — an unusually high-traffic drive, a full tank that wasn't actually filled to the same level as the previous fill, or an odometer reading error can all skew a single measurement meaningfully. Tank-to-tank tracking, recording odometer reading and litres filled at each fill-up over multiple cycles, averages out these one-off distortions and produces a mileage figure that better reflects genuine average fuel efficiency across normal, varied driving conditions rather than one specific drive or one specific fill. This calculator stores fill-up history locally in your browser (not sent anywhere), so mileage tracked over weeks or months of normal driving builds toward a much more reliable number than any single tank estimate could give.
A worked example
A single tank filled right after a long highway trip might show noticeably better mileage than the vehicle's actual typical average, since highway driving is generally more fuel-efficient than city driving with frequent stops — relying on that one measurement as "my car's mileage" would overstate real-world efficiency for someone who does mostly city driving day to day, which is exactly the kind of distortion that tracking multiple fill-ups across mixed driving conditions corrects for.
How this connects to your other vehicle costs
An accurate, tracked mileage figure — rather than a manufacturer's claimed or an optimistic guessed number — is the single input that most affects the accuracy of the Fuel Cost Calculator and the Running Cost Comparison calculator, since both depend directly on mileage to convert distance into fuel cost.
Common mistakes
Estimating mileage from a single fill-up, especially right after an atypical drive (a long highway trip, unusually heavy traffic, a period of unusually light or heavy vehicle load), and treating that one-off number as a reliable long-term average is the most common mistake — track several fill-ups across normal, varied driving before trusting a mileage figure for cost planning.