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Fuel Log and MPG Tracker
Enter each fill-up's odometer reading, fuel amount and price, and the tracker works out the MPG of every tank, your long-run average, cost per mile and monthly fuel spending. Works in MPG, UK MPG or L/100 km, for as many vehicles as you like.
Last updated:
Example fill-ups are shown so you can see the charts.
MPG per tank
Fuel spending by month
Fill-up history
| Date | Odometer | Distance | Gallons | Price | Total | MPG | Cost/mi | Delete |
|---|
Saved only in this browser. Download a CSV now and then as a backup.
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How to use the Fuel Log and MPG Tracker
- Fill the tank up and note the odometer reading, the gallons (or liters) and the price.
- Add the fill-up: enter date, odometer, fuel and either the price per gallon or the total paid, keep Filled the tank up ticked, and press Add fill-up.
- Repeat at every fill-up. From the second full tank on, each row shows that tank's MPG and cost per mile.
- Partial fill or forgot one? Untick Filled the tank up for a top-up, or tick I missed logging the previous fill-up so a gap does not distort the numbers.
- Review the summary and charts, switch units or vehicles, and download a CSV for your records or taxes.
The full-tank method, step by step
| Fill-up | Odometer | Gallons | Full? | What the log calculates |
|---|---|---|---|---|
| 1 | 41,250 | 11.2 | Yes | Starting point, no MPG yet |
| 2 | 41,568 | 10.6 | Yes | 318 mi ÷ 10.6 gal = 30.0 MPG |
| 3 | 41,726 | 5.0 | No (top-up) | No MPG; 5.0 gal carried forward |
| 4 | 41,916 | 6.9 | Yes | 348 mi ÷ (5.0 + 6.9) gal = 29.2 MPG |
Average MPG over the whole log is total measured miles ÷ total measured gallons (here 666 ÷ 22.5 = 29.6 MPG), not the average of the per-tank numbers, so long tanks count more than short ones.
Unit formulas used
- US MPG = miles ÷ US gallons (1 US gal = 3.785411784 L).
- UK MPG = miles ÷ (liters ÷ 4.54609).
- L/100 km = liters ÷ kilometers × 100. Lower is better. L/100 km = 235.215 ÷ US MPG.
- Cost per mile = fuel cost of measured tanks ÷ miles measured.
Tips for accurate numbers
- Use the same pump click-off. Stop at the first automatic click each time instead of topping off; consistent fills give consistent MPG.
- Read the odometer, not the trip meter. The odometer never resets, so a missed entry cannot scramble your distances.
- Expect variation. Winter fuel blends, cold starts, short trips, heavy loads, roof racks, tire pressure and highway speed all move MPG from tank to tank. Watch the average line on the chart for real trends.
- A sudden drop is worth a look. If MPG falls noticeably for several tanks in a row, check tire pressure, the air filter and whether a dashboard warning light is on.
Frequently asked questions
How is MPG calculated?
MPG = miles driven ÷ gallons used. With the full-tank method, you fill up completely, and at the next full fill-up the miles since the last full tank are divided by the gallons it took to refill (plus any partial top-ups in between). The first full fill-up is the starting point, so it has no MPG of its own.
Why is my first fill-up blank?
There is no earlier full tank to measure from, so the first full fill-up only sets the starting odometer. MPG appears from the second full fill-up onward.
What if I only put in a few gallons?
Untick Filled the tank up. A partial fill has no MPG of its own; its gallons and cost are added to the next full fill-up, so that tank's MPG and cost per mile are still correct.
What if I forgot to log a fill-up?
Tick I missed logging the previous fill-up on the next entry. The tracker then starts a fresh measurement from that fill-up instead of spreading the unlogged fuel's miles over the wrong number of gallons, which would show an impossibly high MPG.
How is cost per mile worked out?
Cost per mile = the money spent on fuel for measured tanks ÷ the miles driven on them. It covers fuel only; insurance, maintenance and depreciation are extra.
How do I convert MPG to L/100 km?
L/100 km = 235.215 ÷ US MPG (or 282.481 ÷ UK MPG). The tracker stores distances and fuel precisely and converts automatically when you change Units; UK gallons are 4.54609 liters and US gallons are 3.785411784 liters.
Is my fuel log private?
Yes. All fill-ups are saved only in your browser's local storage on this device and nothing is uploaded. Download a CSV regularly as a backup, especially before clearing browsing data.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.
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