[BigCinBigD]

What would I be if my grand father was 1/2 Indian?

[MadMax, the Grinning Reaper]

His grandson. More likely 1/8th or 1/16th, depending on how they count the two grandfathers/grandmothers and parents.

[sarasmom]

“What would I be if my grand father was 1/2 Indian?”

That depends upon your grand fathers tribe, and your own sex.

Most tribes are matrilineal.
In my tribe, if your grandmother was a 1/2 breed,and your mother was a 1/4 breed, you would be 1/8 and considered tribal, but as a male...you would not automatically be eligiable for legal tribal status, it would require a special ruling.
But if you had a sister, she would be considered tribal, based on her direct bloodlines.

Different tribes vary. Some few are patriarchal.

Ask your grandfathers tribe of your personal legal standing in his tribe.