How this works
Two simple sums sit behind this. For real consumption, divide the litres you filled by the kilometres driven and multiply by 100 — that’s litres burned per 100 km. For cost, multiply that consumption by the price per litre. The price changes daily and by station, so it stays an editable field rather than a fixed number that would go stale fast.
- 1
Pick a mode
"Tank to tank" measures real consumption from one fill-up. "Known consumption" starts from a figure you already have (from the spec sheet or an earlier calc).
- 2
Enter the numbers
In tank mode: km driven and litres you put in. In the other: consumption in L/100km. In both, check the price per litre — it’s editable.
- 3
Read the results
You get consumption (L/100km), cost per 100 km and cost per kilometre. Add a distance and it also totals the trip cost.
Frequently asked
How do I work out my car’s real consumption?
Fill the tank to the click, reset the trip meter to zero, drive as usual, and at the next fill-up top it to the click again. The litres it took are exactly what you burned. Divide litres × 100 by the trip km and you get L/100km. This beats the on-board computer, which tends to read optimistic.
Which price per litre should I use?
Whatever you actually paid, or the average near you. We hardcode no value because the price changes daily and by station. DGEG publishes every station’s price at precoscombustiveis.dgeg.gov.pt — check it and type the number in. The default shown is just a starting point.
What’s the difference between L/100km and km/L?
Same thing upside down. Portugal uses L/100km: how many litres to cover 100 km, so lower is better. km/L (common in Brazil and the US) says how far one litre takes you, where higher is better. To convert, divide 100 by the consumption: 6 L/100km is 16.7 km/L.
Does the advertised (WLTP) figure match real life?
Rarely. The WLTP figure on the spec sheet is measured in a lab under controlled conditions. On the road — wind, A/C, traffic, a heavier foot — real consumption usually runs 10% to 30% higher. That’s why this tool has the "tank" mode: it measures what the car burns with you driving, not in the brochure.
Is my data stored anywhere?
No. Every calculation runs in your browser. Nothing is sent to our servers or anyone else’s, and nothing is saved when you close the page.
DISCLAIMER
Results are an estimate based on the numbers you enter. Fuel price varies by day, station and type (diesel, petrol 95/98). Check the current price at DGEG and confirm against your own fill-up. This tool is not financial or mechanical advice.