Depends on the weight and the style of axe, and the way you want to use it.
Very, very broadly:
Hatchet - 600g head - 350 mm handle (as low as 300mm, as high as 400mm)
Small axe - 800 - 1000g head - 500 - 600mm handle (as low as 450mm, as high as 700mm)
Big axe - 1000 - 2500g head - 800mm handle (as low as 650mm, as high as 900mm)
Carving axes and broad axes tend to be on short handles - a Gransfors broad axe is about 1500g, 500mm handle.
Have a look at good toolshops and websites to get some ideas, see if local styles of axes were handled in particular ways.
(I was going to post in Imperial measurements, but I see you are in Italy so maybe metric is better for you?)
Cheers