Fuel Economy Log
Log fill-ups per vehicle and chart your km/L fuel economy trend by week, month, and year.
Loading your fuel log…
Use on any page (bookmarklet)
Want Fuel Economy Log without leaving the page you're on? Drag the button below to your bookmarks bar, then click it on any website to open Fuel Economy Log right there — it runs entirely in your browser.
Use responsibly: a bookmarklet runs on whatever page you click it on. Avoid sensitive sites such as online banking, payment, or healthcare pages — you run it at your own risk. Everything is processed locally and no data is sent anywhere. See our Terms.
- Show your bookmarks bar if it's hidden — Ctrl+Shift+B (⌘+Shift+B on Mac).
- Drag the button above onto the bookmarks bar.
- Open any website and click the bookmark — the Fuel Economy Log panel appears in the top-right corner. Use ✛ to move it between corners, or ›/‹ to tuck it against the edge and pull it back out.
- Click the bookmark again (or the ✕) to close it.
Note: a few sites with strict security policies may block bookmarklets.
Examples
Two fills
Input
10,000 km / 40 L, then 10,500 km / 38 L
Output
500 km ÷ 38 L = 13.16 km/L this tank
Monthly average
Input
Several June fills
Output
June average charted at, say, 12.8 km/L
Two cars
Input
Sedan + SUV
Output
Separate logs and averages for each
About this tool
This free fuel economy log tracks your car's real-world mileage over time. Log each fill-up — the date, your total odometer reading, and the litres added — and it builds your average km/L and L/100km and charts the trend by week, month, or year. Run more than one car? Add each as a separate vehicle with its own log. Everything is saved on your device and works great on a phone at the pump.
How to use
- Pick a vehicle (or add one) at the top.
- Each time you fill the tank, enter the date, total odometer (km), and litres.
- After two or more fills, see your average economy and the trend chart.
- Tap the chart points to read each period's exact figures.
The full-to-full method
Economy is measured between fills: the fuel you add at a fill covers the distance driven since the last one. So fill the tank fully each time and record the total odometer — the first fill just marks your starting point, and every fill after that adds a data point to your average and chart.
Frequently asked questions
How does the fuel log work?
Each time you fill up, log the date, your total odometer reading (km), and the litres you added. The tool works out the distance between fills and the fuel used (the full-to-full method) to calculate your economy in km/L and L/100km, and charts how it changes over time.
Can I track more than one car?
Yes. Add as many vehicles as you like and switch between them — each keeps its own separate log and average. This matters because economy is based on odometer distance, which only makes sense within one car's own readings.
Why do I need the total odometer, not the trip distance?
Using the total odometer at each fill lets the tool measure the exact distance between two fills automatically, even if you forget to reset a trip meter. Just read the big total-kilometres number on your dashboard each time you fill up.
What does the chart show?
It plots your average km/L over time — grouped by week, month, or year — so you can spot trends, like better economy in summer or after a service. Hover or tap a point to see that period's exact average and distance.
Is a lower or higher L/100km better?
Lower is better — L/100km measures how much fuel you burn to cover 100 km, so a smaller number means a more efficient car. It's the opposite of km/L, where higher is better. The log shows both.
How do I get accurate results?
Always fill the tank completely each time and record the total odometer and litres. One tank can be misleading, so the average over several fills — which the log builds up automatically — gives the truest picture.
Is my data saved or uploaded?
Your vehicles and fill-ups are saved only in your own browser (localStorage). Nothing is uploaded or shared, and clearing your site data removes the log.
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