Two cars say “40 MPG”—but are they using the same gallon?
The letters can match while the measurement differs. Know the gallon convention before comparing a listing or dashboard.
Put it into practice
Try the tool Fuel Economy: L/100 km & MPG · Free, with local processing.
The short answer
The letters can match while the measurement differs. Know the gallon convention before comparing a listing or dashboard.
The Fuel Economy: L/100 km & MPG helps you turn the inputs into an estimate you can inspect. The useful part is understanding which assumption drives the answer, rather than treating the largest number on screen as a decision by itself.
Work through an example
Using 45 L over 600 km gives 7.5 L/100 km, approximately 31.3619 US mpg or 37.6641 Imperial mpg.
The example uses explicit inputs so you can reproduce it. Replace them with your own measurements or assumptions, and keep the units consistent. A result can be arithmetically correct while answering the wrong question if the inputs describe something else.
Use this checklist
- Record kilometres travelled and litres used over the same interval.
- Distinguish US from Imperial gallons when reading an MPG figure.
- Compare similar driving conditions rather than treating one tank as a fixed vehicle property.
How the calculation works
L/100 km = litres used ÷ kilometres × 100. MPG = miles travelled ÷ gallons used. US gallons are 3.785411784 L; Imperial gallons are 4.54609 L.
The tool shows its result and supporting values together. Where an item must be bought or counted in whole units, read the rounded count as well as the underlying quantity. Display rounding is separate from real-world uncertainty.
The mistake to avoid
US and Imperial MPG are different. Tank-to-tank comparisons need a consistent fill level; a single journey may not represent typical driving.
Compare at least one realistic alternative input before making an important purchase or plan. If the result looks surprising, inspect the units, the source of each input, and what the calculation leaves out first.
A useful next step
Open the Fuel Economy: L/100 km & MPG to try the example. You can also explore Trip Fuel Cost & Split for the next part of the workflow. The related tool is optional; using one estimate does not mean you need to make a purchase or change your routine.
Reference and scope
Natural Resources Canada: consumption units provides background on the method or measurement convention. ToolMallow is not affiliated with that publisher. Product, institution and individual circumstances can differ; use the limitations above alongside the result.
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