Sorry for the late reply on this! I've had a look at the pattern in my copy of that issue. The fabric requirement is for 4m, measured on 140cm wide fabric. That said, it's REALLY long! I've just measured one of my mid-calf length coats, and the full back length is 92cm. I'm just under 5'5" in height. The Burda trench coat is 120cm long - that would be ankle length on me! I usually need to take out anything between 3cm and 4cm from the sleeve length, so all those length adjustments would mean I needed far less than the full stated amount.
You can also do a cheat if desperately want to use the fabric you have and have another similar one. The upper back will be covered by the storm flap (which has a lovely curve to it, by the way) and not cut the whole of each back in one piece, but substitute something else for what lies under the storm flap, if that makes sense. You could also piece the front facings at the bottom, where it won't show so much. One thing to watch out for, though, is the self fabric belt - they always take a surprising amount of fabric. You can reduce how much you need for it by making it a buckle up belt rather than a tie one, as the buckle version needs less fabric.
With a bit of devious planning, you might just manage it.