Gas Mileage Calculator
Enter the distance you drove and the fuel you used to get your MPG, L/100 km and km/L. Plan the fuel cost of a trip and keep a log of fill-ups to track your average.
Tip: fill the tank, reset the trip meter, drive, then fill up again. The fuel you put in the second time is the fuel used.
Trip cost planner
Fuel economy is filled in from your result above. You can type your own.
Fill-up log
Press “+ Log fill-up” to keep each tank in this list. It is saved in your browser so you can track your average over time.
| Date | Distance | Fuel | Economy | Cost |
|---|
How to use the Gas Mileage Calculator
- Choose your units: US gallons, UK imperial gallons or metric liters.
- Enter the odometer readings at start and end, or switch to Trip distance and type the miles or km.
- Enter the fuel used and, if you like, the price per gallon or liter.
- Press Calculate to see MPG, L/100 km, km/L and the cost per mile or km.
- Plan a trip or log the fill-up to estimate a journey's cost or track your average over time.
How to calculate gas mileage (MPG)
Fill the tank and note the odometer. Drive as usual, fill up again and note the odometer and the amount of fuel you put in. Then:
- MPG = miles driven ÷ gallons used
- L/100 km = liters used ÷ kilometers driven × 100
- km/L = kilometers driven ÷ liters used
Example: the odometer goes from 12,000 to 12,300 miles and the second fill-up takes 10 US gallons. That is 300 ÷ 10 = 30 MPG (US). In metric, 300 miles is 482.8 km and 10 US gallons is 37.85 L, so 37.85 ÷ 482.8 × 100 = 7.84 L/100 km, or 12.75 km/L. Because an imperial gallon is bigger (4.546 L), the same car does 36.03 MPG (UK).
MPG to L/100 km conversion chart
To convert, use L/100 km = 235.215 ÷ MPG (US) or 282.481 ÷ MPG (UK). A higher MPG is better, while a lower L/100 km is better.
| MPG (US) | MPG (UK) | L/100 km | km/L |
|---|---|---|---|
| 15 | 18.01 | 15.68 | 6.38 |
| 20 | 24.02 | 11.76 | 8.50 |
| 25 | 30.02 | 9.41 | 10.63 |
| 30 | 36.03 | 7.84 | 12.75 |
| 35 | 42.03 | 6.72 | 14.88 |
| 40 | 48.04 | 5.88 | 17.01 |
| 50 | 60.05 | 4.70 | 21.26 |
How to work out the fuel cost of a trip
Fuel needed = trip distance ÷ MPG (or distance × L/100 km ÷ 100), and trip cost = fuel needed × price per gallon or liter. For a 250-mile drive there and back (500 miles) in a car that does 30 MPG, you need 500 ÷ 30 = 16.67 gallons. At $3.50 a gallon the trip costs $58.33, or $29.17 each if two people share it. The cost per mile is simply the fuel price divided by the MPG: $3.50 ÷ 30 = about 11.7 cents a mile.
Tips for an accurate reading
A single tank can be misleading because pumps click off at slightly different levels. Log several fill-ups and use the average, which the fill-up log works out as total distance divided by total fuel rather than an average of averages. Fuel economy drops in cold weather, with short trips, heavy loads, roof boxes, underinflated tyres and high motorway speeds.
Frequently asked questions
How do I calculate my gas mileage?
Fill your tank and note the odometer. When you next fill up, note the odometer again and the gallons you added. Divide the miles driven by the gallons. For example 300 miles on 10 gallons is 30 MPG.
How do I convert MPG to L/100 km?
Divide 235.215 by the US MPG figure. 30 MPG (US) is 235.215 ÷ 30 = 7.84 L/100 km. For UK MPG, divide 282.481 by the MPG.
Why is UK MPG higher than US MPG?
An imperial gallon is 4.546 liters while a US gallon is 3.785 liters. The same car goes further on the bigger UK gallon, so its UK MPG is about 20% higher than its US MPG.
What is good gas mileage?
For a modern petrol car, 30 MPG (US) or better, about 7.8 L/100 km, is good. Hybrids often reach 45 to 55 MPG, while large SUVs and pickups may get 15 to 22 MPG.
How do I work out the fuel cost of a trip?
Divide the trip distance by your MPG to get gallons, then multiply by the price per gallon. The trip planner does this, can double the distance for a round trip and split the cost between passengers.
Where is my fill-up log stored?
Only in your browser's local storage on this device. Nothing is uploaded. Clearing your browser data or using a different device starts a fresh log.