Practical guide
Fuel consumption, journey cost and tire size — how are they calculated?
Automotive calculators combine measured data with simple geometry. A result helps compare consumption or dimensions but does not replace vehicle documentation or technical assessment.
Consumption needs a complete measurement
A good simple measurement uses fuel added to a comparable fill level and distance since the previous fill. Divide litres by kilometres and multiply by 100.
For multiple full-tank intervals divide total litres by total kilometres, not an unweighted mean of row rates. The initial full tank starts measurement; combine partial refills through the next full tank.
Journey cost uses forecast consumption
Required litres come from distance and l/100 km, while cost uses your manually entered price. Enter one-way distance in the calculator; round-trip mode doubles only that distance.
Enter tolls and parking for the whole trip. Split the total equally per person if needed; depreciation and maintenance are excluded.
Tire size describes geometry
Notation such as 205/55 R16 gives width, profile percentage and rim diameter. Nominal diameter affects circumference and the speedometer relationship.
Similar diameter does not confirm approval or fitment: check rim width, offset, load and speed ratings and clearance.
Frequently asked questions
What does this guide explain about “Consumption needs a complete measurement”?
A good simple measurement uses fuel added to a comparable fill level and distance since the previous fill. Divide litres by kilometres and multiply by 100. For multiple full-tank intervals divide total litres by total kilometres, not an unweighted mean of row rates. The initial full tank starts measurement; combine partial refills through the next full tank.
What does this guide explain about “Journey cost uses forecast consumption”?
Required litres come from distance and l/100 km, while cost uses your manually entered price. Enter one-way distance in the calculator; round-trip mode doubles only that distance. Enter tolls and parking for the whole trip. Split the total equally per person if needed; depreciation and maintenance are excluded.
What does this guide explain about “Tire size describes geometry”?
Notation such as 205/55 R16 gives width, profile percentage and rim diameter. Nominal diameter affects circumference and the speedometer relationship. Similar diameter does not confirm approval or fitment: check rim width, offset, load and speed ratings and clearance.
Calculators covered by this guide
Tyre size comparison calculator
Compare nominal tyre dimensions, without assessing rim fitment.
Fuel consumption calculator
Calculate average fuel use in litres per 100 kilometres.
Fuel and trip cost calculator
Calculate fuel, tolls and parking with an equal per-person share.