Normally, if you take the float bowl off while it is full it will be 2/3 of the depth of the bowl. This depth is controlled by the little float valve at the tang on the back of the floats, and by how clean and well-sealed the float valve is with its seat.
Some here will recommend the "clear tube" method: if you go that route, the fuel level should be 2-3 mm below the top of the float bowls when sitting on the bike with the gas ON and the fuel tank above the RESERVE level.
