For circumnavigation you should be able to motor at least 25% of the distance. It is better to assume 30%.
I have no idea what the poster possibly could be thinking, but as others have said, this bears no resemblance to a reasonable approximation of reality. But beyond that, much of the answer revolves around the choice of boat and the choice of comfort level, since that impacts fuel consumption. For example, if you are of the 'all the comforts of home' school of thought, I can't think of a sub-50 foot boat that carries enough fuel to run air conditioning for a long passage.
At the opposite end of the spectum, the "go spartan- go now" school of thought, almost no fuel is required, especially when combined with a decently performing boat. An example of that school of thought was conversations that I had with two separate owners of sisterships of my boat.
The one had sailed from Capetown S.A. to the Caribbean. That boat was equipped with a windvane for steering, did not use refrigeration, would switch in the GPS 4-5 times a day and record coordinates. ran a tri-color at night, ran the engine well less than an hour every 3-4 days to recharge the batteries and that was only in cloudy conditions when the solar panel could not keep up, and made the trip on less than 12 gallons of fuel, less than 60 gallons of water, and averaged 150 miles a day for the entire trip. That might not be viewed as a normal passage since the first 10 days was spent broad reaching and running up the coast of Africa in 30-50 knot winds. Once things lightened he angled across the South Atlantic below the Doldrums to the South American Coast where he close reached in the adiabatic winds until north of the Doldrums.
The other couple with a sistership, went non-stop from South Africa to Scotland. They used closer to 25 gallons of fuel but motored part way through the Doldrums. If I remember correctly they carried roughly 40 gallons of fuel (two 13 gallon tanks plus gerry cans on deck). In flat water, these boats will motor at roughly 6 knots at a 1/2 gallon an hour so arguably they had at max a roughly 240 mile range. They had refrigeration that used an engine driven compressor and cold plates so arguably they had less range.
I would not even conjecture what the other end of the spectrum looks like.