Ad blue Alert - US and UK gallons incorrect compared to litres ..why ?

[lucky13]

So i’m getting an Ad blue alert for 2.5 UK gallons, if I go into the settings and change the units to US gallons it still says I need 2.5 US gallons which should be completly different but it doesn’t seem to think so, but if I go into units and change it to UK litres then it suddenly becomes 8.75 litres …what on earth is going on and which figure do I use as nothing makes sense!!!

For info:

2.5 UK gallons is 11litres
2.5 US gallons is 9.6litres

 

[Bigsidavies]

I've always just looked at the higher figure in gallons multiplied by 8 and then divided by 2 which puts you roughly in the middle of the required range. Worked for the last 70k miles.