How much fuel is there when it reaches half?

How much fuel does it contain when it reaches half the mark of fuel indicator of honda dio?

.8 gal or 3 litres.

Who knows? What is the shape of the tank? Most fuel tanks are not symmetrical, and the fuel guage works off a float, so half is going to simply be halfway between the top and bottom of the tank… Not a precise measurement in any tank that is not perfectly symmetrical top to bottom.

What does the owners manual say the capacity is? Easy test then would be to get it to half tank, fill it up, and subtract the amount of fuel it took to fill, from the stated capacity.