I am at approximately 13700km and have averaged 10-11L/100km which would give me a total fuel usage of 1370-1507 litres. 2000-3000km of the 13700km were below -10C so no def usage would have occurred.
I have used approximately 10 gallons (37.8L) of def which is less than the 3% (41.1-45.21L) I think your supposed to use.
My math could be wrong but my tank was filled at the dealer pre sale, I added another 5 gallons and just the other day added about 4 gallons and it still reads full.
I think def usage is supposed to be in the 3-5% range. It also depends on your driving style, freeway driving should use less def as there is enough heat generated by the combustion process to self clean the filters I’ve read.
3% of 145 gallons is 4.35 which is about right comparing it to my usage.
Also my def gauge is very unreliable under 1/2 a tank, you can watch the needle go up and down as you drive sometimes as much as a quarter tank in 20-30 seconds.