UK MPG calculation is wrong

S tu 5 years ago • updated 5 years ago 4

I have entered 5 dummy fill-ups to get used to the functionality of the app & to confirm my local values (UK miles travelled, litres fill-up & mpg) are supported but am presented with an incorrect average mpg figure.

Basic data entered:

Fillup 1 - 126463 miles, 28.03 litres to full

Fillup 2 - 127000 miles, 32.00 litres to full, 76.35mpg

Fillup 3 - 127500 miles, 28.00 litres to full, 81.18mpg

Fillup 4 - 127750 miles, 14.00 litres to full, 81.18mpg

Fillup 5 - 128300 miles, 40.00 litres to full, 62.5mpg

A total of 1837 miles (app shows 1836!) & 142.08 litres of fuel.

While the between fill-ups mpg is corect, the average shown by the app is 73.25mpg wheras actual is 58.784mpg!

A last gripe is that, even though I select  my preferred mileage log date format, the default is still shown on all charts & also the export csv is very basic compared with other apps & also shows lp100 not my local UK mpg figures.

Apart from that, fantastic app!



I've checked your values. 

Total mileage: Yes. This is probably because of some roundings in my app. And one mile is missing.

Your fuel consumption is correct. You can check other apps but 73.25mpg (uk) is correct.

I need to check date formats. Date in CSV should be always in ISO format (yyyy-mm-dd).

CSV export is only for backups (at the moment) but I'm thinking about creating special reports.

Thanks for looking into this so promptly however, I'm still not sure about the average fuel consumption figures.

Total miles covered 1837 - Total litres of fuel used 142.03 which converts to 31.25 UK gallons.

Therefore 1837 miles divided by 31.25 UK gallons gives 58.784mpg not 73.25.

I have entered the exact same figures in another app (Easy MPG) & 58.8mpg is returned.

I think the problem is with the initial fill-up. If I deduct the fuel from this (28.03 litres - 6.17 UK gallons) I get 1837 miles divided by 25.08 UK gallons which gives 73.246mpg! Should this fuel be used as part of the equation or is it for 'show' only as the initial amount required to fill the tank? I think I'm confusing myself with this.



The app you have tried probably also is doing it wrong.It was fixed some time ago. This is a little bit tricky. Many people think.

The right data you need to use to calculate real fuel consumption (for your example is):

1837 - this is good!

142L - this is bad. 

114L - is good for your example

You can't use: 1837 and 142.03l to calculate avg fuel consumption.

1837 and 142 - 28(!) which is 114. This is the real fuel you've used. You can't use fuel from the first fill-up for that. 

Makes perfect sense now. Many thanks for taking the time to explain this to me.

Hope to see this fantastic app. continue to develop. I shall certainly be looking to upgrade to the pro version in due course!