Driving style and usage habits play a big role in your car’s fuel consumption figures. Heavy traffic will result in dire mpg readings while long motorway runs can give surprisingly good results.
In order to save as much money as possible on fuel, you need to have an idea of your own car’s fuel consumption so that you can monitor how it changes in different situations.
For tips on improving fuel consumption, check out our seven top mpg tips.
How to Calculate MPG
Here’s how to calculate fuel consumption in mpg (miles per gallon):
Fill up your car’s fuel tank until the fuel pump cuts off.
Reset the trip meter reading on the dashboard, so you can record how many miles you do until the next fill up.
Drive normally until you next need to fill up.
Fill up the tank up completely again and make a note of how many litres of fuel you put in.
After fuelling, make a note of the reading on the trip meter before resetting it again.
Now you should have two numbers – the number of miles since you last filled up, and the number of litres you have just put in your car’s fuel tank.
Use this formula to calculate mpg:
No. of miles / No. of litres * 4.54 = mpg
400 miles divided by 30 litres multiplied by 4.54 = 60.5mpg
This method provides a good guide to fuel consumption and is accurate enough for most purposes. However, don’t get carried away with calculating your exact fuel consumption (e.g. 45.465mpg) – you cannot measure mileage or fuel used that accurately.
Using Your Car’s Trip Computer To Monitor MPG
If your car has a trip computer that provides a mpg reading, then I would suggest using this to monitor your fuel consumption. Critics of these computers say that they are not 100% accurate, but they are accurate enough, and more importantly they are consistent. This means that you will be able to see if your average fuel consumption is rising or falling – and that’s all that really matters.
Here’s a quick guide to using a trip computer to monitor fuel consumption:
Your car may have several mpg readings – for example, an average mpg figure and an instantaneous reading. Trip computers vary – find out what information yours provides (check the manual).
To monitor mpg, you need an average reading of some kind. You should be able to reset this if you want to start a new mpg test, or can simply leave it forever and just monitor whether it gradually rises or gradually falls.
If your mpg gradually rises, then your driving style has improved and you are using less fuel. Congratulations!
Finally, if your car’s computer provides an instantaneous mpg reading, this can be useful too. This will show you what your mpg is at that moment – so you can experiment with changing your driving habits to improve it. For example, you may find you can change gear a little earlier than usual to stop fuel consumption peaking so high when you are accelerating.