Published figures are a starting point, not an answer. Consumption depends on the load the engine is actually carrying — hull, propeller, fouling, sea state and the rpm you hold — so two identical engines in different boats will burn quite different amounts.
Use the model's fuel curve to get an expected figure at the rpm you cruise at, then measure the real one. The reliable method is to log fuel added against hours run and rpm held over several trips, or to run a measured passage at a steady rpm and refill to the same point. A flow meter or engine data on a multifunction display shortens the work considerably.
Once you have litres per hour at a cruising rpm, range follows: usable fuel divided by litres per hour, multiplied by the speed you hold. Usable fuel is not tank capacity — subtract what the pickup cannot reach and hold a reserve, typically a fifth or more for weather, tide and diversion.
Recalculate after antifouling, a propeller change or a repower. Those change the numbers more than most owners expect.