That's a big kohlrabi! When I had kohlrabis, I would harvest them at about half that size. Actually, I would cut of some of leaves and cook them up long before I would take the kohlrabi itself. The leaves are very good to eat if you cut them off when they are young and tender. If you wait too long, they become woody, as does the kohlrabi.
Dear Wife won't eat any kohlrabi, so I gave up growing them. I like the taste, mainly raw with some ranch dressing. But I was the only one eating them and it was too much for me all at once. Last year, I think half of my kohlabi was wasted. Well, nothing gets wasted. I'm sure I fed it to the chickens. But I would rather use my garden space for things both Dear Wife and I enjoy, so this year, sad to say, kohlrabi was off the list.