Car Fuel Consumption
ConvertEverything runs locally in your browser — nothing is uploaded
Enter the distance driven, the fuel added and the price, and you get four ways of stating consumption plus the cost per kilometre. The two systems run in opposite directions. Most of the world uses L/100km — lower is better; the US uses MPG — higher is better. Reading only the number leads to the opposite conclusion, so both are given and the note says which way is better. The UK also uses MPG, but not the same gallon. An imperial gallon is 4.546 L and a US gallon 3.785 L — 20% apart, so the same consumption reads 20% higher in UK MPG. Both are listed, each labelled. The conversion constants are derived, not copied. The factors between MPG and L/100km (235.2 US, 282.5 UK) are easy to misremember, so they are computed here from the unit definitions — 1 mile = 1.609344 km, 1 US gallon = 3.785411784 L, 1 imperial gallon = 4.54609 L — and a test pins the well-known landmark: 8 L/100km ≈ 29.4 MPG (US).
Features
- All four: L/100km, km/L, MPG (US), MPG (UK)
- ⚠️ Notes that MPG and L/100km run in opposite directions
- ⚠️ Keeps US and UK MPG apart (the two gallons differ by 20%)
- Cost per km and per 100 km, with an editable fuel price
- Conversion constants derived from unit definitions, pinned by a test at 8 L/100km ≈ 29.4 MPG
- Computed locally
How to use
- Enter the distance driven (or the range covered on one tank)
- Enter the fuel added and the price
- All four consumption figures and the cost per km appear
- For a running log, change the distance and fuel and recompute
FAQ
- How do MPG and L/100km convert? Why do the numbers look so different?
- They are inversely related, so there is no fixed multiplier: MPG (US) = 235.215 ÷ (L/100km). 8 L/100km ≈ 29.4 MPG and 12 L/100km ≈ 19.6 MPG. They also run in opposite directions — lower L/100km is better, higher MPG is better. UK MPG uses the imperial gallon (4.546 L), 20% larger than the US gallon (3.785 L), so the same consumption reads 20% higher in UK MPG.
- Why does this differ from the figure on my dashboard?
- That is normal, and they are two different things. The dashboard figure is estimated by the trip computer from injector duty, and it tends to be optimistic (idling and cold-start enrichment are hard for it to account for). What is computed here is measured: distance between two fill-ups against the fuel added. For accuracy, use tank-to-tank: fill up and note the odometer, then at the next fill-up divide the fuel added by the distance covered. A single run is heavily affected by whether the tank was actually full, so averaging over several tanks is more reliable.
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