A practical test is often best for answering this. E.g. fill the tank up, go cruising for a while logging engine
hours (try to keep at the same sort of revs), speed & conditions, then see how much juice it takes to top up again. But the consensus from previous replies seems to be something in excess of 200nm, and much more if clean & sail assisted in light seas.
often have specific fuel consumption
curves that you could use to estimate range. Such curves allow you to do much better than our guesswork. If yours has one, measure your speed at different revs and then work out e.g. range at 80% revs or revs giving you maximum range.
Just carry a jerry can if you don't know and are off on a long trip ...